bug 839552 - ignore generated file icc.json; r=fabrice

*build/applications-data.js* generates *apps/settings/resources/icc.json*, so *.gitignore* should ignore it to suppress spurious "untracked files" warnings by Git after building Gaia:

```
02-08 09:45 > git status
# On branch master
# Untracked files:
#   (use "git add <file>..." to include in what will be committed)
#
#	apps/settings/resources/icc.json
nothing added to commit but untracked files present (use "git add" to track)
```