Added choosing first day of the week (#19)

[Aga-C]

What is it?

• Bugfix
• Feature
• Codebase improvement

Description of the changes in your PR

• Added a dialog for choosing first day of the week to any day.
• By default, first day of the week is:
  • If a user in the old version of the app had set an option that Sunday should be first, Sunday will be set as a first day. Code for that is in MainActivity and can be removed in the next version after releasing this one.
  • If there wasn't anything set earlier, it will use the default first day of the week for current locale (same as in Calendar).
• Modified the sorting by day logic to consider different first days of the week. Also, simplified that logic a bit.
• Modified the alarm edit dialog to sort days properly.

Before/After Screenshots/Screen Record

qemu-system-x86_64_I2iSfeKKHL.mp4

Fixes the following issue(s)

• Fixes Allow setting first day of week to any day #19

Acknowledgement

• I read the contribution guidelines.