Fix city label & note locations

[Qrox]

Sometimes city label and note's background and text do not strictliy align, when the overmap font and normal font has different sizes or when overmap window size is not dividable by the tile size.

This fixes it by:

1. Correctly implement string drawing. The ch parameter of OutputChar is assumed by Font classes to be a single utf-8 encoded unicode codepoint. Passing a string to OutputChar incidentally works, but the drawing position need to be hacked to correctly position the string, and OutputChar may render text incorrectly if characters after the first one needs to be drawn with a fallback font. There are also some android-specific code that needs to be updated to use draw_string, but I don't have the environment to test it, so I'll leave it for @ZhilkinSerg.
2. Use utf8_width to get the correct print length of strings.
3. Center city labels, and left and top-align notes.
4. Use font instead of overmap_font, because the code uses fontwidth and fontheight which are font's properties.
5. Mark "Notes: " to be translated.
6. Remove some unused variables.

[GoLoT]

I think I'm done with my changes so there shouldn't be any new conflicts from now on. I'll merge as soon as you resolve the conflicts unless you want me to do it.

[Qrox]

I've rebased the changes.