Stop using private implementation details of the `formatter<std::tm>`.
We never needed anything from the class besides the format specifier,
which is easily obtainable with public API.
Introducing new tooltip placeholder: {timezoned_time_list}. It will be replaced with the list of times in different time zones.
I've found it useful to hover the mouse pointer on time and see time in all my timezones at once.
Current timezone excluding from the list, so if you will scroll over the time module and change the active timezone, this timezone will be excluded from the list and the previous active zone will be added.
After this refactoring:
1. Timezones parses only once on start and the we refer to saved values. All time_zone.isString() checks gone to the constructor.
2. Single timezone case handling as case of multi timezoned logic.
3. Scroll event seems more clear now.
4. Tooltip template parses on start to check if there calendar placeholder or not. To do not calculate calendar_text() if not necessary.
Also fixed timezones behavior: now waybar starting with the first timezone in timezones list and falling back to timezone field only if timezones omit or has no elements.
There was one uninitialized value warning and two mismatched-sign
compare warnings. They both appear valid, the first occurring when MPD's
"format-stopped" contains {songPosition} or {queueLength} and the second
occurring when the clock's "timezones" array is more than 2 billion
items long (not likely, I admit). Fix both issues.
