Return a moment for dates from tasks model

[raimund-schluessler]

Cloning a moment is 8x faster than creating a moment from a date object. This code

	const iterations = 1000
	const t0 = performance.now()
	for (var j = 0; j < iterations; j++) {
		var tmp = moment(task.due)
	}
	const t1 = performance.now()
	console.debug(`This took ${t1 - t0} ms.`)

	const t2 = performance.now()
	for (var j = 0; j < iterations; j++) {
		var tmp = task.dueMoment
	}
	const t3 = performance.now()
	console.debug(`This took ${t3 - t2} ms.`)

prints

    This took 116.985635 ms.
    This took 15.836432000000059 ms.

I don't know, if this really has a measureable effect on the App itself, but it shouldn't make it slower for sure.

[codecov]

Codecov Report

Merging #713 into master will increase coverage by 0.2%.
The diff coverage is 40.74%.

@@            Coverage Diff            @@
##           master     #713     +/-   ##
=========================================
+ Coverage   26.46%   26.66%   +0.2%     
=========================================
  Files          44       44             
  Lines        2086     2104     +18     
  Branches      386      386             
=========================================
+ Hits          552      561      +9     
- Misses       1417     1426      +9     
  Partials      117      117