Have some input fields retain focus until there is a click signal

[bentoogood]

Users have reported issues with the strict 'focus-follows-mouse' rule, especially when entering a field to input text (users let go of mouse/pen to type, which causes pointer to move out of panel and switch focus to another panel)

One suggestion for addressing this is to have some fields use the older 'click-to-set-focus' policy.
Fields that should follow this rule include all numeric and text entry widgets. Two large offenders are the expression editor, and the script editor - so make sure multi-line text input fields are covered

[johnhaddon]

We had also discussed drawing a focus border around the Viewer and NodeGraph rather than doing this. Has it been decided that this new ticket is definitely the way forward instead?

[bentoogood]

It'd be good to try the visual indicator first, but I wanted to get this down before I forgot about it.
If highlighting the active panel proves effective we could bump this one way off into the distance.
Will put in another ticket for the border highlight.

[johnhaddon]

I think fixing this would also fix #439.