Provide flexibility for Maghrib / Fajr times

[mr-islam]

As suggested by brother Konto by email,

can you add the feature to manually write in maghrib and fajr time? People might be following different opinions on times than the ones shown in the app.

Great suggestion and more doable, instead of trying to add other Calc methods to the UI. (That'll only be worth doing when we have more international Calc methods)