Test for issue #20

[Homescreen] Write test to access and exit edit mode
updated with assertRaises
updated according to code review
replaced assertRaises with assertEqual
improved _delete_app_locator
Updated TODO message
Merge remote-tracking branch 'mozilla/master' into issue_20
Test delete a contact for #493
Removed remove_confirm.py, move RemoveConfirm class into contact_form.py.
Merge remote-tracking branch 'mozilla/master' into issue_493

Conflicts:
	gaiatest/tests/contacts/manifest.ini
Merge remote-tracking branch 'mozilla/master' into issue_493
Modified locators from xpath to css selector.
Merged `RemoveConfirm` into `EditContact` class.
Merge remote-tracking branch 'mozilla/master' into issue_20
Redesigned asserts due to zac's comments
Merge pull request #411 from AlinT/issue_20

Test for issue #20
Add test_edit_mode to manifest.ini
Merge pull request #516 from zacc/issue_20

Add test_edit_mode to manifest.ini
Move test_wallpaper.py into settings/ folder
browser app object
remove xfail Bug 850658
Merge pull request #498 from bebef1987/browser_app

browser app object
Merge pull request #518 from bebef1987/remove_xfail

remove xfail Bug 850658