Periodically execute calendar sync

Write a cronjob that executes the following commands for tasks with projects:

1. Browse to the folder with calendar synchronization files.

cd ~/maintenance/gCal/

1.a Loop through all tasks

1.b Identify/list all projects, (e.g. uni.int.as and uni.int.ex as different projects).

1.c Loop through list with all projects

1.d Assign the project (name) as tag to all tasks in that project.

task status:pending proj:uni.int modify +uni.int

task status:pending proj:uni.rep modify +uni.rep

1. Then sync all tasks with (google) calendar using the tags to calendars.
   
   2.a Note, distinguish calendars up to 2 dots in the project name. E.g. both tasks uni.int.as and uni.int.ex go into a (new) calendar named: TW uni.int.
   
   ./tw_gcal_sync -c "TW intern" -t "uni.int"
   
   ./tw_gcal_sync -c "TW represInterac" -t "uni.rep"

3. If you want you can expand this method by asking the user whether they want custom calendar names e.g. TW intern in stead of `TW uni.int`. 

Start in the calendar synchronization directory ~/maintenance/gCal/ and read the existing ./tw_gcal_sync command and its -c and -t options. Trace how Taskwarrior project tags map to calendars, then define the cron entry around the listed task commands; done means pending tasks are grouped by project and synced to calendars with the specified two-dot naming rule.

Written by the indexing model from the issue text.