1. Don't allow mention invalidation by altering mention with mouse or keyboard
2. Don't allow mention duplication on the same position
3. Clean mentions after text with mentions changes
4. Fix mention selection
5. Make sure mention is separated by text with valid separators (we're using only space)
6. Cursor will consider the mention as an object and will jump over it as it would be a single character (placing cursor inside leaves room for mention invalidation)
