Fixes & improvements to Subtitle Chooser

[svobs]

• I have read CONTRIBUTING.md
• This implements/fixes issue The Find Subtitle Result Window was too Narrow to see the whole name. #4057.

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Description:
Like #4825 but makes additional changes:

• The message osd.sub_found, previously set to %d subtitles found. Downloading…, was not exactly appropriate as the heading for the list of subtitles to download. It looks like this is was done because it was being reused for the actual "downloading" message. So I changed the existing message to remove the Downloading… part, and added a new osd.sub_downloading message whose English version is Downloading %d subtitles, and changed the "downloading" message to use this key instead.
• Improve text size of sub-heading and table items slightly
• Change table style & border so it looks like this mock-up from @Iiii-I-I-I. Also implemented some other changes to displayed attributes based on said mock-up:
• Remove time from upload date (seems rare that subtitles are uploaded more than once a day).
• Remove rating (seems to be 0.0 most of the time?) - am open to bringing this back
• Add release year in parentheses.
• Add up to 2 fraction digits to fps attribute's displayed value.