For #3865, show extensions that failed to start up with an error message
For #3868, properly convert backslashy paths back to Unixy paths on their way back from Node
For #3861, hide Browse Extensions button while installing
For #3859, use padding instead of text-indent to position text in search box
For #3866, set a height on table cells so they don't shrink smaller when a button is removed
Merge pull request #3874 from adobe/nj/extman-bug-fixes

Bug fixes for extension manager