Replace event types concept with calendars

[naveensingh]

Checklist

• I made sure that there are no existing issues - open or closed - to which I could contribute my information.
• I made sure that there are no existing discussions - open or closed - to which I could contribute my information.
• I have read the FAQs inside the app (Menu -> About -> FAQs) and my problem isn't listed.
• I have taken the time to fill in all the required details. I understand that the request will be dismissed otherwise.
• This issue contains only one feature request.
• I have read and understood the contribution guidelines.

Feature description

Replace any occurrences of the term "event type" with "calendar" and rework any functionalities that rely on a distinction between these terms.

Why do you want this feature?

• Improved UI/UX
• The app uses both terms interchangeably, e.g., "Manage synced calendars" vs "Manage event types", which is inconsistent.

Additional information

Click to see user-facing event type strings

• "Event types"
• "Manage event types"
• "Default event type"
• "Select an event type"
• "Default event type cannot be deleted"
• "Move affected events into the default event type"
• "Manage quick filter event types"
• "You have filtered out all event types"
• "Include event types"
• "Ignore event types in the file, always use the default one"
• "Holidays have been successfully imported into the "Holidays" event type"
• "Holidays created that way are inserted in a new event type called "Holidays". You can go in Settings -> Manage Event Types, long press the given event type and delete it by selecting the trashbin."
• "How can I modify or delete an existing event type?"
• "You can do both of those in the app Settings - Manage event types. Just click on the wanted one for changing the label and color, or select the wanted one by long pressing it and use the trashbin at the top menu for deleting."

There may be more.

The "Store locally only" and "Select event type" options in the event editor should be unified into one option listing all calendars - local and otherwise.

[SamGreenwood1]

I'd ideally want both. So I could for example have my school calendar with event types for assignments, classes, etc.