fix(mdUtil): remove/delete cacheFactory keys when clearing/destroying cache

`mdUtil`'s custom `cacheFactory` factory, adds/removes keys when
putting/removing a single key, but leaves `keys` untouched when calling
`removeAll()` or `destroy()`. As a result, the following problems arise:

- Keys of destroyed caches continue to take up memory.
- The `keys()` method return incorrect results after calling `removeAll()`
  (i.e. it continues to return the old keys, although they are not present
  in the cache any more).

This commit fixes these issues, by overriding the `removeAll` and
`destroy` methods as well.
fix(mdMedia): avoid unnecessary digest and make changes apply quicker

Previously, the `updateAll()` method relied on `$timeout` for scheduling a
digest. This made the possible changes apply after the next rendering and
could possibly lead to extra digests.

This commit, replaces the call to `$timeout` with a call to `$evalAsync()`,
which avoids an extra digest if one is already in progress and also applies
the changes before the next rendering.
test(mdMedia): add more tests and move .spec file to correct location

In commit 6397040 `mdMedia` was moved out of the `sidenav` component and into
`core`. The .spec file remained in the original folder though.

This commit moves the 'media.spec.js` file to the correct location and
adds more tests to more thoroughly cover `mdMedia`'s functionality.