Added feature to prevent users from sending empty messages

[seshagiriprabhu]

As mentioned in #60, GUI freezes upon pressing either Enter or Return key for a long time. This feature prevents user from sending blank messages. Well the .pro file which was added automatically along with this commit is awful. It was automatically added. I cloned again and made changes and pushed again and it was again automatically added to my pull request.

[nurupo]

@seshagiriprabhu you made a PR to the wrong repo and if you want to commit a specific file, just do git commit -m "message" ./file/to/commit1 ./file/to/commit2 ./etc
Also, the freeze of GUI is caused not by pressing Enter directly, but by messages that get created in the message display widget. We would like to prevent users from sending empty space messages, so your PR is fine. Just remove the .pro file from the commit and submit it to the right repo : )

[Schlumpf]

Merged to nurupo/ProjectTox-Qt-GUI