Move regex from delegates to C++ model

[minimoog]

Because qml delegates are dynamically instantiated (created and destroyed depending if they are in the listview), regexing to determine links, tags, and mentions should be moved to corresponding C++ model. Regexed text of the tweet should be also stored in the model.

This will remove unnecessary regexing when delegate is instantiated in the view.

[minimoog]

Not easy fixable. Delayed solution for future versions.