Removes max number of photons constant

As photons are no longer stored in an array, it no longer serves a
purpose.
Uses list size to determine number of photons

This frees us of the need to update the number of photons in the
underlying StFmsCluster - the photon list will be resized as photons are
added or removed.
Returns number of photons from list size

This avoids having to keep a separate counter updated whenever the list
changes length.

Note that this necessarily changes how we loop over the photons in the
maker class, as the cluster hasn't had its photon list populated yet at
the time we loop.
Deletes number of photons setter method

Deletes the separate field storing the number of photons, as this value
is now returned from the photon list.
Replaces parameter C-style array with STL array
Uses aggregate initialisation
Replaces parameter C-style array with STL array
Replaces float value with double

Renames variable for greater clarity.

Results in slightly altered numerical output from increased float
precision.
Replaces C-style array with STL array
Changes geometry methods from float to double

Knocks on to some other classes that depend on geometry information.
Changes return type from float to double
Changes return types from float to double
Changes variable types from float to double
Replaces all floats with doubles
Deletes outdated comment