improvements to file browsing and form feedback
adding more instructions to inputs
fix for empty browse file form
merge
remove weird file preview
add hint for map ID
proper grammar
add instructions for composite sources:
Store bookmarks based on model id. Closes #228
Merge pull request #227 from mapbox/formbrowse-improve

Formbrowse improve
Styled scrollbar on bookmark list
Tweaks to the bookmark list when content is overflow
Merge branch 'master' of https://github.com/mapbox/tm2
cleanup map controls
Merge branch 'master' into interaction-tab-help