Implement lumi skipping for Online DQM Input Sources.

In several cases some lumisections won't appear in our storage,
in such case, we should start processing the next available lumisection.

This commit implements a flag _nextLumiTimeoutMillis_.
If it is set, each missing lumi will start a timer.
After the timer is triggered, and if and only if the next lumi is
available, the source will switch to that lumi.

For example:

1. nextLumiTimeMillis is set to 45000
2. we see files ls0001 ls0002 ls0005
3. source processes ls 1 and 2
4. 45 seconds pass
5. source skips 3..4, and starts processing ls0005

This commit also changes how EoR files work: instead of relying on EoR
content, the source uses the highest *seen* lumi as the number of lumis.
This is compatible with our code in offline and online (where EoR are,
for now, empty).
Merge pull request #4634 from dmitrijus/LumiSkipping

Implement lumi skipping for Online DQM Input Sources.