Moved several hard-coded UI strings to strings.xml

I noticed some strings were not localised when my phone was set to French, and then realised that these strings were actually hard-coded. So I moved them all to strings.xml, which also required some minor code changes to get the context in scope, in order to fetch the string in some cases.
Not needed indeed, but I feel it makes the code more succinct and clearer since the context is used three times in this method.

If I don't put it in a variable the next lines would give the following, which I don't find as easy to read...
pd.setMessage(GroupCreateActivity.this.getString(R.string.GroupCreateActivity_loading_group_details));
pd.setMessage(GroupCreateActivity.this.getString(R.string.GroupCreateActivity_please_wait));

Thoughts?