strings in the zoom options don't have context for what is high/low any more

• "low"/"high" for brightness and contrast may need different words in some languages
• the strings "thick"/"thin" and "full" are not reused, but don't have the context that they are for the crosshair and color. they currently have the wrong gender in the ukrainian translation

there are these contexts in the .po files but they are no longer used in the code:

#~ msgctxt "universal access, color"
#~ msgctxt "universal access, brightness"
#~ msgctxt "universal access, contrast"