Index ResourceLoader dependency lists in startup

By using the existing indexes of modules in the array being passed to
mw.loader.register we can reduce the size of the startup module by about
6% after gzip (nearly 20% before) on a wiki with very few modules (such
as my localhost). Comparing data from en.wikipedia.org shows about 9%
after gzip (nearly 30% before).

The technique adds a function to mediawiki.js which resolves the indexes
before registering the modules, which costs a little bit of data in that
payload, but it's negligible (118 bytes after gzip) in comparison to the
overall reduction.

Also, cleaned up lies in documentation and strange use of "m" as an
iterator variable.

Bonus: fix ISO8601 timestamp instead of UNIX timestamp being passed
to custom loader scripts.

Change-Id: If12991413fa6129cd20ceab0e59a3a30a4fdf5ce
Merge "Index ResourceLoader dependency lists in startup"