Better autodetection of Soft Tabs.

Check for the presence of a space, instead of the absence of a tab.
This ensures that Soft Tabs will not be activated on a file that (for
example) starts with a BOM or something, but is otherwise full of hard
tabs.
merge latest upstream master
updated regex in usesSoftTabs to only look for Tab and Space
Added linux open-folder keybind.
Moved application:open-dev to `ctrl-alt-o`
Merge pull request #3409 from syndbg/master

Added linux open-folder keybind.
Focus existing window after opening path
Upgrade to tree-view@0.113
Merge pull request #3369 from khakionion/master

Better autodetection of Soft Tabs.
:memo: :lipstick:
:lipstick:
Return a boolean like the comment says
Return undefined to ? fallback works
Document undefined case
:racehorse: Use direct comparison instead of regex
Upgrade to language-go@0.17