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
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
import the fallback variables in the base theme