Added create blog/group items to blog/group spinners.

briar-android/res/values/strings.xml

...android/src/net/sf/briar/android/GroupNameComparator.java

...ndroid/src/net/sf/briar/android/blogs/LocalGroupItem.java

.../net/sf/briar/android/blogs/LocalGroupItemComparator.java

.../net/sf/briar/android/blogs/LocalGroupSpinnerAdapter.java

...src/net/sf/briar/android/blogs/WriteBlogPostActivity.java

briar-android/src/net/sf/briar/android/groups/GroupItem.java

.../src/net/sf/briar/android/groups/GroupItemComparator.java

.../src/net/sf/briar/android/groups/GroupSpinnerAdapter.java

...c/net/sf/briar/android/groups/WriteGroupPostActivity.java