series.js: remove jquery and convert to typescript

[freyavs]

This pull request removes all jquery from series.js and converts it to typescript. It also fixes some small bugs.

Fix 1: a small bug for the css on activities: before, when adding pending and new to an activity tr-element, this didn't have any effect on the css. Now when adding pending or new, the opacity is correctly changed (in the short time frames it takes to add an activity to a series):

Before (when pending):

After (when pending):

Fix 2: I also made sure that a user can't add/remove the same activity multiple times. This was possible when it was taking a longer time for adding/removing an activity (e.g. waiting on a response), so these changes are only visible for this edge case. For adding, the add button was not hidden when a series is being added (in the new and pending stages). The add button only became hidden when the series was successfully added. This made it possible to add multiple instances of the same activity. The new flow is

• the add button gets hidden directly, and becomes visible again on addingActivityFailed
• For removing, the remove button gets hidden (see image below), and becomes visible on removingActivityFailed.

Before (when pending):

After (when pending):

This is progress on #3590

[jorg-vr]

Code looks good :) Thanks for the bug fixes!

Just found one small extra improvement, which we might as well include while we're busy refactoring this code

[bmesuere]

(I would wait to merge this one till after the exams)