Ability to create Custom quest anywhere

[mnalis]

As noted by @meiphoo7-Mae in #679 (comment), it would be useful to be able to create Custom quest anywhere on the map, even in places where nothing is currently mapped.

Currently, one is only able to create Custom quest by:

• manually crafting .csv file outside of SCEE -- but that is complex and hard to do on the mobile while on the ground
• in SCEE in response to regular quest via Uh... / Can't say / Create custom quest -- but that requires existing quest (and thus eligible existing OSM elements) to be present there already.

Use case
quoting from that comment:

In the area where I map several redevelopment projects are going on that will at least take the next five years to complete, so I would like to use the custom quest to remind me about certain things that I should survey (even if there are no existing regular quests nearby). Creating a public note makes no sense and is polluting the map because apart from a few random users that occasionally come by I'm the only mapper in the area.

Proposed Solution
When long pressing on the map, in the menu add another option Create custom quest. It would do exactly the same thing as Uh... / Can't say / Create custom quest does (when invoked as an answer to existing quest), but would not require existing quest. (just like long press + Create new note differs from Uh... / Can't say / Leave note.

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Current ugly workaround to accomplish that is:

• long press to Add POI (or use Things overlay)
• add e.g. bench
• on a "backrest quest" (which you must have enabled) choose Uh... / Can't say / Create custom quest
• enter a message to be shown for custom quest
• undo the "Add bench"

That leaves the user with just a custom quest, but it ugly and prone to errors (e.g. leaving random nonexistent benches around, or undoing too much, etc.)