Add stability message for Atom.io API

This indicates that the Atom.io API is not frozen - this is describing the state
of things, not announcing a new policy.
Move gutter member into a showLineNumbers observe block
Change shift-delete to trigger core:cut

Win32 and Linux keymaps
Check that args are present before mapping over

Closes #2925
Upgrade to language-javascript@0.35
Upgrade to metrics@v0.33.0
Upgrade to fuzzy-finder@0.57.0
Upgrade to apm@0.77
Prepare 0.115
Upgrade to tree-view@0.109.0
Upgrade to markdown-preview@0.91
Upgrade to markdown-preview@0.92
Update git-diff to fix atom/git-diff#31
Upgrade to markdown-preview@0.93
Prepare 0.116
:memo: Add missing :
Add spec for loading theme with incomplete variable file
Add cssForFile to LessCompileCache
Load packages with the fallback variables
Load fallback variables in the user’s stylesheet