R22 LLP-related backported bug fixes

This collects together several backported bug-fixes, which impact LLP analyses, for a Run 2 data reprocessing The fixes, except for the last two below, are cherry-picked from later commits. The last two were re-written since the original commits relied on too many conflicting changes. A few modifications were made, eg ignoring changes to CA configs or files that didn't exist in original branch. DATREP-281 tracks the developments.

Branch	Bugs
R22-LLP-CherryPicks-DATREP-281-LRT_Elec_Fix	MR !56568 (merged) and !57358 (merged); Electron d0 bug
R22-LLP-CherryPicks-DATREP-281-cellAssocLRT	MR !59679 (merged) and !60425 (merged); Cell association for LRT
R22-LLP-CherryPicks-DATREP-281-cellLink	MR !52256 (merged); LRT egamma cell link
R22-LLP-CherryPicks-DATREP-281-muonTruthAlgs	MR !49898 (merged) and !49833 (merged); Muon truth algs on LRT
R22-LLP-CherryPicks-DATREP-281-MuonSegments	attempt at fixing LRT muon segment links
R22-LLP-CherryPicks-DATREP-281-rebased-mergeStaus	Backported ext merger of ID cands into Stau reco
	MR !66869 (merged) Pix+TRT alignment conditions for mixed LBs
R22-LLP-DATREP-281-LRTElectronIsolation	Calo iso for LRT El, avoids 'large cluster' bug in AOD

Squashing is not enabled as these should be kept separate for better bookkeeping.
I've rebased everything so that the commit history is clean.