New features, some of them solving open issues

I have implemented some features that people usually  request to Support Force Team:

1. **Confirmation when creating a new secret chat:** according to issue #241
2. **Confirmation when sharing contact info:** As it is an option that appears on top of chat when contact don't know your number, I think (and so do some other member of Spanish Support Force) that it is a good idea to ask for confirmation, to avoid unintentionally clicks.
3. **Only wifi Automatic Download:** As an option in settings for Audio and photos, according to issue #146. It can also be helpful to save data, when then people, like me, have a limit of 1GB or even less.
4. **Add Version Info in Settings:** A new section have been added in settings (at the bottom) that shows currently version name, according to issue #391.
5. **Show/Hide Last Connection:** This is the hardest one because with current API the only way (the one I used) is to avoid client sending "online" notification to servers, so other users can't know if I am online; they will only know the time when I decided to hide it as my "last connection time". According to this, this feature is client dependent so if using another client without this feature, this client will send "online" info and contact wil know it.
6. Finally I added some strings needed to strings.xml (in English and Spanish).

There are some changes in *build.gradle* that I needed in order to compile my app correctly, but don't think they are needed in official version (except changing version number).