add -a to indexthemes task to index custom themes

Gulp won't index the custom directory of not -a or -t is passed with the command.
Merge pull request #666 from malles/patch-1

add -a to indexthemes task to index custom themes
Fixes #675
Fixes #679
Fixes #672
Merge branch 'develop'
removed duplicated component less files
Fixed dropdown z-index #521
changelog updated
Merge branch 'develop' of github.com:uikit/uikit into develop

Conflicts:
	CHANGELOG.md
Fixes #674
typo
updated version
compiled docs js
updated readme
updated readme
fixed css loading order in tests
cleanup vendor folder