Allow devs to remove from Tarako marketplace (bug 1053230)

https://bugzilla.mozilla.org/show_bug.cgi?id=1053230

App is shown to Tarako:
![screenshot 2014-09-04 15 44 02](https://cloud.githubusercontent.com/assets/211578/4156436/57fd8104-3474-11e4-9b94-2d197a8780e3.png)
After clicking the remove button:
![screenshot 2014-09-04 15 44 27](https://cloud.githubusercontent.com/assets/211578/4156439/5d2b23ca-3474-11e4-9646-e2c4571c96f8.png)
After confirming the removal:
![screenshot 2014-09-04 15 31 39](https://cloud.githubusercontent.com/assets/211578/4156379/c782d188-3473-11e4-9c3c-c93498df3831.png)