TTSManager: Fix modality of voice TTS settings dialog

[lumpidu]

The voice TTS settings activity had a wrong modality option when opened. Change intent flags from FLAG_ACTIIVITY_NEW_TASK to FLAG_ACTIVITY_NO_HISTORY.

This will change the behaviour like this:

• open activity on top of the TTSManager activity
• close activity when navigating back
• close activity when resuming by navigating back to Símarómur from another app / activity

This fixes / closes #143