Make tab and tabset context menus extensible

Update code for creating context menus to use *-menu-items triggers.
Add :order key so item order can be specified by other plugins or
behaviors.
Update rem-tabset def to remove compiler warning
Fix this variable reference in tab-menu-items
Merge remote-tracking branch 'lighttable/master' into extensible-menus

Conflicts:
	deploy/settings/default/default.behaviors
	src/lt/objs/tabs.cljs
Rename tabset menu items trigger
Add object for tab label

Adds an object for the tab label so that the right click menu can be
extended with the :menu! and :menu+ triggers. Also allows use to reuse
the :lt.objs.menu/menu! behavior and reduce code duplication.
Make $ and $$ multi arity

Reduces the number of warnings generated by the cljs compiler.
Add multiple fonts support
Merge current master into pull request branch
Merge pull request #1391 from mortalapeman/extensible-menus

Extensible menus
Merge pull request #1441 from ykomatsu/master

Add multiple fonts support
Dont walk forward when editing find bar
Add docs and blog posts to readme
One more post
linux_deps.sh: If 'which curl' fails, exit with its return code.
linux_deps.sh: re-use downloaded LightTableLinux*.gz, clojure-plugin

* download LightTableLinux*.tar.gz only if it doesn't exist and always
  verify its sha1 checksum.
* store clojure-plugin as a git-submodule and clone it only once. Then
  update it with git pull --rebase
git-ignore deploy/core/node_modules/
Fix WARNING: Wrong number of args (1) passed to lt.object/specificity-sort
update-listeners is always called with instants == nil
Fix WARNING: Wrong number of args (3) passed to lt.object/raise*