MDL-49817 grunt: Refactor the uglify task
This is in preperation for the watch task and doing a few things:
1) Switch away from 'grunt.file.expandMapping' to the declarative syntax
for doing the same thing, as recommended in docs:
http://gruntjs.com/api/grunt.file#grunt.file.expandmapping
2) Factor the renaming function into shared function so it can be used
from the watch task too.
3) Shared the file glob'ing pattern for match AMD js files between
jshint and uglify task (this removes the node_modules exception..
we should add it to both if we need it).
4) Rename the task configuration - I am just doing this because it looks
like 'dynamic_mappings' is some how magic config option when you
look at the manual:
http://gruntjs.com/configuring-tasks#building-the-files-object-dynamically
But in fact, it's just a task confguration name.
