Added basic firefoxOS support

Added firefoxOS to the compatibility list as suggested in #91
It prepares the firefox OS platform as expected.
Now if someone could create tests and add a way to automatically generate the [manifest.webapp](https://developer.mozilla.org/en-US/Apps/Build/Manifest) file from the phonegap config, it'd be great.

Output of `grunt build` as requested:

```
[4mRunning "clean:tasks" (clean) task[24m
Cleaning tasks...[32mOK[39m

[4mRunning "clean:test" (clean) task[24m
Cleaning test...[32mOK[39m

[4mRunning "copy:test_fixtures" (copy) task[24m
Created [36m2[39m directories, copied [36m37[39m files

[4mRunning "copy:test_cordova" (copy) task[24m
Copied [36m1[39m files

[4mRunning "coffee:tasks" (coffee) task[24m

[4mRunning "coffee:test" (coffee) task[24m

[4mRunning "readme_generator:readme" (readme_generator) task[24m
[32m>> [39mGetting package info from options...
[32m>> [39mNo need to get package info...
[32m>> [39mGenerating banner to place on the very top...
[32m>> [39mGenerating table of contents, you won't get lost...
[32m>> [39mDigging the past for release information...
[32m>> [39mGetting the latest changelog from the changelogs folder...
Your readme file "README.md" is ready!
[32mOK[39m

[32mDone, without errors.[39m
```

Thanks