fix preview-images with alt-text / "outside"-method

[Drezil]

Similar to #79 in affected areas - but way more lightweight.

Problems i had:

• Images with alt-text got selected, but linked incorrectly.
• As i use "outside" as method the folder-path was always missing

solution:

• drag method into FolderBrief-constructor
• cut off | and everything after in [[…]]-links
• view.sourceMode.cmEditor does not exist anymore in obsidian-api-master and moved to view.editor. Both work in my version, but typescript kept complaining until i fixed it :grin:

compiled it with rollup and it worked for me.