Clean up TowerFit

Reduce whitespace, unused headers, move members to private if possible
Set FitTower geometry in constructor

This was set manually by Yiqun later, but all the information is there
for it to be done in the FitTower constructor.
Add Doxygen comments to FitTower
Add optional error arguments to PhotonHitFPD

Add after existing arguments, with the same defaults as before, to
maintain backward compatibility.
Move setting of photon parameters to FitTower

It is simpler to do this in one place in FitTower, than in two places in
Yiqun. It also keeps things more encapsulated - FitTower has a simple
input (towers) and a simple output (photons) rather than making
downstream code deal with a complicated set of fit parameters.
Move Minuit config steps to constructor

Set values once, rather than once per fit, if the settings should not
change fit-to-fit.

Remove configuration steps that set values that are already the default
(e.g. SET ERR).
Move photon parameter setting for 2-photon fit

Modify 2-photon cluster fitting so it follows the same pattern as the
general function i.e. FitTower::Fit2Pin1Clust takes a photon list that
it populates from the fit parameters directly, rather than filling
parameters in Yiqun
Remove FitTower::SetFCN

Never called by any other code
Remove FitTower::pTowerUtil

TowerUtil object was allocated but never used.

Also some formatting edits in the FitTower header.
Tidy FitTower functions

Namely FGams, GGams, Fcn1, Fit, Fit2Pin1Clust, Fcn2.
Add comments and rename and rearrange some parts for clarity.

Also remove fNumbPhotons member as it is no longer used.
Remove x and y tower widths from FitTower

These members are never used in the code any more
Change TMinuit in FitTower from pointer

Doesn't require dynamic allocation, so it saves some code (and the
chance to leak memory in case of an exception in the constructor) to use
a regular instance

Also make the TMinuit private as it is not longer needed externally by
Yiqun (all minimisation-related code is now contained in FitTower).
Move includes from FitTower header

Only leave those that are needed, use forward declarations where needed.

Add TowerFPD include to Yiqun as it didn't include it itself (only via
FitTower, which no longer has it in header)
Put FitTower source in namespace

Also remove ClassImp statement, as these are no longer needed