EGAM derivations: new formats for HI, and fix a few small bugs

Implements EGAM11 and EGAM12, custom versions of EGAM1 and EGAM7 for heavy ions, as requested in https://its.cern.ch/jira/projects/ATLEGAMDPD/issues/ATLEGAMDPD-230

To make this run, EGammaCommon sequence has been modified so that forward electron ID and isolation density tools are only run after checking that needed containers are available in input (they are missing in HI AODs).

Also fix a little potential bug in each EGAM format in which code would break if thinning is not done because a variable was defined only inside a conditional statement.

Finally fix also another bug showing up in the test heavy ion AOD where clusters have been thinned away in the input (discussed with @jdevivi couple of weeks ago).