figure out what to do with index timestamp when using per-project indexing

[vladak]

After #1390 it will be possible to figure out which projects are indexed. The timestamp displayed at the bottom of the page reflects latest index, be it partial (per-project) or across all projects. Thus, the timestamp can be broken into per project timestamps. The only remaining thing to solve is how to reflect these in the UI.

[tulinkry]

1. put it instead of current version column
2. reorganize the table to include the date for each project
3. use a tooltip on hover at some element in the table
4. make a modal window with useful information (current version, last timestamp, ...) on click on some element in the table

More over when viewing specific project there could be an info at the bottom:

Last Index update for ABCD Mon Jul 17 16:20:00 CEST 2017
Last Index update Tue Jul 17 16:20:00 CEST 2022

[vladak]

In our case it is sufficient if the timestamp reflects that all projects are indexed, so we do this:

/opengrok/dist/bin/sync.py --messages=/opengrok/dist/bin/Messages --indexed --workers 16 --config /opengrok/etc/sync-config.json -p
touch /opengrok/data/timestamp