New preferences: Colors

Few years ago I've added a torrent name highlighting feature that applies colors based on tracker list status. But these colors were hardcoded bcs there are no place in app's settings for them. And there were no user-accessible description of these colors meaning.

This merge request introduces a new preference page: Colors. It contains the settings I want plus I added a few settings for adjusting default green/red torrent name highlighting and adjusting colors of good/low share ratio. Just bcs now I have place for them. (Note: although share ratio colors are on Colors preferences page the min value of good share ratio are still set in another place. I also changed its ToolTip a bit).

In fact, the color controls were copied from "Info Widget" preferences. Info Widget is a plugin that may be disabled so its color settings can't be moved to the new preferences page.

There is also an additional "reset" button that resets colors to their hardcoded default bcs global button resets all settings which is too much. I hardcoded the defaults bcs there is no way to get them via KCoreConfig API.

One thing that warring me most is wording and spelling for settings description and ToolTips.