Bug 1087441: Apply font fix to FMD panel header. r=arthurcc

I'm afraid that there is no similar code in settings app as this file is currently a mix of AMD module and legacy code.

My intention was to make the file easier to be included in the unit test. We need to do the following:
- Remove `findmydevice_loader.js` as it is redundant.
- Define the `findmydevice` module as described in the previous comment, and load the module when l10n is ready. 
By doing this we can easily require the module that we want to test (`findmydevice` in this case) by loading `findmydeivcejs`. It also give us a chance to replace the modules that we want to mock.