Bugfixes: StartButton

### TimestampActivity

* Startbutton
 * The Startbutton should now be reset properly when removing a "running block"
 * The running block no longer "follows" when the user changes day.
 * Disabling/Enabling the Startbutton now works properly.

* Removed some unecessary code.

### Block
* Made a method that checks if a block is stopped.