MathEditor Kellyroach/fix warnings

This pull request fixes assorted Xcode 9.4.1 compiler warnings.

IPHONEOS_DEPLOYMENT_TARGET = 8.0 This change extends support down to iOS 8.0 from iOS 9.2 and avoids yellow warnings regarding 8.0 versus 9.2 linkage to iosMath .
Xcode 9.4.1 Update to recommended settings
Fix 'Block implicitly retains self' yellow warning
Fix 'Dead Store' Analyze issue
Fix 'nil returned from a method' Analyze issue
Fix another 'nil returned from a method' Analyze issue
Fix 'Could not load the keyboard-marine-pressed image' runtime error Capitalization issue in MTKeyboardTab3.xib Use Keyboard-marine-pressed with uppercase K .

We filtered iosMath Analyze issues by modifying Podfile at start of our commit trail, then restoring original Podfile before we branched at end of our commit trail. Our recently approved and merged P.R. #103 on the iosMath repo addresses the iosMath Analyze issues not addressed by the current P.R. here.

We tested MathEditor on our branch just before and just after restoring original Podfile . The app functions OK in both tests. The difference is we do see remaining iosMath Analyze issues after restoring original Podfile because our P.R. #103 changes to the iosMath repo haven't been issued a release on COCOAPODS.ORG yet.

Jul 13 '18 03:07 kellyroach

TEST: before restoring original Podfile

2 Analyze targets --> "No issues" PASSED
Build and Run app on "iPhone X" simulator Entered x/y+x^y >= 3.14159 and it looks OK PASSED

TEST: after restoring original Podfile (current state of our P.R. branch)

Analyze --> "3 warnings, 25 analyzer results" which all seem to be from "Analyze target iosMath" as expected. There is a good chance most or all of these will go away after next release of iosMath to COCOAPODS.ORG, assuming it contains our P.R. #103 on the iosMath repo changes. Without our changes in current P.R. we will get "4 warnings, 28 analyzer results".
Build and Run app on "iPhone X" simulator Entered x/y+x^y >= 3.14159 and it looks OK PASSED

Jul 13 '18 03:07 kellyroach

Product > Test before restoring original Podfile

Test Suite 'MTDisplayEditingTest' passed at 2018-07-12 21:06:33.929.
	 Executed 5 tests, with 0 failures (0 unexpected) in 0.079 (0.082) seconds
Test Suite 'MathEditor_Tests.xctest' passed at 2018-07-12 21:06:33.930.
	 Executed 5 tests, with 0 failures (0 unexpected) in 0.079 (0.083) seconds
Test Suite 'All tests' passed at 2018-07-12 21:06:33.930.
	 Executed 5 tests, with 0 failures (0 unexpected) in 0.079 (0.085) seconds

Product > Test after restoring original Podfile

Test Suite 'MTDisplayEditingTest' passed at 2018-07-12 21:09:18.971.
	 Executed 5 tests, with 0 failures (0 unexpected) in 0.057 (0.059) seconds
Test Suite 'MathEditor_Tests.xctest' passed at 2018-07-12 21:09:18.972.
	 Executed 5 tests, with 0 failures (0 unexpected) in 0.057 (0.060) seconds
Test Suite 'All tests' passed at 2018-07-12 21:09:18.973.
	 Executed 5 tests, with 0 failures (0 unexpected) in 0.057 (0.062) seconds

Jul 13 '18 04:07 kellyroach

XCTOOL TEST ON OUR LOCALHOST

2015s-MacBook-Pro:MathEditor kellyroach$ xctool -workspace MathEditor.xcworkspace -scheme iosMathEditor-Example run-tests -test-sdk iphonesimulator
[Info] Loading settings for scheme 'iosMathEditor-Example' ... (733 ms)

=== RUN-TESTS ===

  [Info] Collecting info for testables... (942 ms)
  run-test MathEditor_Tests.xctest (iphonesimulator11.4, iPhone 5s, logic-test)
    ✓ -[MTDisplayEditingTest testClosestPointExponent] (16 ms)
    ✓ -[MTDisplayEditingTest testClosestPointFraction] (0 ms)
    ✓ -[MTDisplayEditingTest testClosestPointFractionPlusRegular] (0 ms)
    ✓ -[MTDisplayEditingTest testClosestPointRegular] (0 ms)
    ✓ -[MTDisplayEditingTest testClosestPointRegularPlusFraction] (0 ms)
    5 passed, 0 failed, 0 errored, 5 total (19 ms)


** RUN-TESTS SUCCEEDED: 5 passed, 0 failed, 0 errored, 5 total **

Jul 13 '18 04:07 kellyroach