Add isOnlyWhitespace()
Invalidate whitespace lines when their indent level changes

Refs #2376
Fix spec name
Little note :memo:
:lipstick:
Tokenize empty lines with a changed indent level synchronously
More specs in tokenized buffer testing empty line retokenizing
:lipstick: naming
Add checks for the change event
Update editor component specs
Remove the awkward _.pick
Merge pull request #2737 from atom/bo-fix-indent-guide

Fix indent guide