Unicode replacements

[Askaniy]

Suggest to replace

• -> with → in sky_chart_teaching_card_detail
• - with − (minus sign) in help_section_instruction5
• - with – (en dash) in help_section_instruction2, help_section_instruction7, widget_next_spacecraft_pass_time_range
• m2 with m² in light_pollution_teaching_card_title_X

Also, I thought %% is needed as escaped character, but I see this doubled percent on Android

[levinli303]

%% is probably for formatted string only. i don't think we have strings that contains percent signs which we need to format

[levinli303]

Fixed in https://github.com/levinli303/astroweather-localization/commit/4443b147e49865e4f4bbdd4a63c1965617e14d0f