Activate FlowIDE when `all` is true

[rafaelrene]

Hi!

Currently I'm working on a project that has set all=true in .flowconfig file, so there's no // @flow in any of the files and as such FlowIDE does not activate at all.

I believe that if .flowconfig exists, FlowIDE should check if all option is present and all features should be activated just like when file has // @flow on top