WIP: Rename all instances of "Kirigami.theme.buttonTextColor" on GUI elements which are not buttons

Although they are the same on many themes, the viewTextColor is probably what was wanted instead of the buttonTextColor when setting the colour of text on the primary-coloured background. It is an unusual use-case, but some users have aggressively non-default theme colours which cause the GUI to draw in the wrong colour. This was noticed by someone testing kdeconnect-sms (which uses a "borrowed" ChatMessage.qml from Kaidan).

There are other instances of buttonTextColor which make less sense to me., I have commented on those where they appear.

I can't really test this because I can't build Kaidan, but I have tested these changes in kdeconnect-sms. Where the same elements were used, the result looks good (but I don't use all elements there)