Ignore additional white-space while adding users to groups

User unable to add new users if there's an addition whitespace at the end of username or email address while adding a user to a Team's users group.
After click Add button, the loading icon will keep spinning and both "Add"&"Cancel" button will be disabled.

Steps to reproduce

1. Navigate to https://bitbucket.org/account/user/<Team-Username>/groups/
2. Click "Add member"
3. Enter email address with an addition whitespace at the end
4. Click the "Add" button