Added the possibility to share a entry via standard Android share intent...

This commit adds the possibility to share a entry via the standard Android share intent.
The text that will be used adapts automatically to the date, meaning:

* TODAY:
```
Today the topic on #Mittwochstreff is "___".  
Everybody is welcome to join. It starts at 19:30.
  ```
* FUTURE:  
```
On dd.MM.yy the topic on #Mittwochstreff is "___".
Everybody is welcome to join. It starts at 19:30.
```
* PAST:  
```
On dd.MM.yy the topic on #Mittwochstreff was "___".
```

``values-de`` strings are also included.

Scrennshot:
![share intent](http://i.imgur.com/HLSkP8u.png)