Give feedback while loading a new week

[marcelm]

Please describe the feature

As a user I want to have some kind of feedback when switching between weeks while the numbers for the current week are being loaded so that I know whether I have a) not filled in the numbers or b) the page has just not finished loading.

Detailed description

After switching to a new week, the times for each day of the week are immediately erased and the totals are set to 0.

This is somewhat irritating in two ways:

• When going to an earlier week that I have filled in, it appears as if all data had been lost.
• When going to a week that I have not filled in, I have to wait a couple of seconds until I can be certain that the site probably has finished loading and that there is indeed nothing filled in.

For me, it takes about three seconds until all numbers are loaded.

A couple of ways in which this could be solved:

• Load the hours faster. It takes about 100ms per activity at the moment.
• Fill in the hours as soon as the data is available.
• Do not set the totals to 0 when switching to a new week, but leave them empty. This makes it clear that no data is available. Then fill in everything at once as soon as all data is available, including totals.
• Show some other type of "Loading ..." indicator.

More info

Related: #646