* HighlightPhrase: Fix wrong documentation
* Use right constructor for new HighlightPhrases
* Fix preset highlights changing unintentionally
Prior to this commit, the callback for reacting to user input on the
highlight table (namely, `HighlightingPage::tableCellClicked`) only
checked for the row number in order to determine whether preset
highlights (self highlights, whispers, and subscriptions) need to be
updated. Hence, changing rows 0 through 2 in the "User Highlights" tab
would also update the preset highlights.
This commit adds a check to determine whether the callback was triggered
by the "Messages" highlight tab, or not.
* Support for user-defined sounds and colors
* Make color & sound columns selectable
* Add custom row for subscription highlights
* Add subscriptions to custom highlights and centrally manage highlight colors
* Dynamically update message highlight colors
