Reduce size of Yiqun

Eliminate members and methods that are not called in our version of the
code.
Begin to reduce length of Yiqun event fitting

This happens in a very long for loop that is hard to follow. Begin by
reducing the amount of whitespace in parts. One- and two-photon fitting
function now return chi2/ndf rather than chi2, as chi2/ndf is all that
is ever used. This also allows shortening of parts of the code in the
loop.
Add additional functions to streamline event fit

Add separate functions to find lowest-energy photon in a cluster and to
match a tower in a cluster. Streamline event fitting code, removing
"bogus photon" flag by just using a NULL result from tower matching to
mean "bogus photon".
Move 2-photon validation to a function

This improves readability of the main function code. Add extra comments
to explain the algorithm.

Replace tab characters with spaces.
Tidy remainder of FitEvent function

Remove the remainder of excessive whitespace. The function is still to
long to easily read, so it should be split into separate functions.
Remove photon array from Yiqun

The photon array is never used in our code, despite being filled. All
photons are accessible via their respective clusters anyway.

Add photon numbers at the end, rather than keeping track of the count at
various points during the fitting algorithm.
Use pointer arguments for tower fitting

There was a mixture of reference and pointer arguments in tower fitting
code. Now consistently use pointer arguments for tower lists when the
list is modified in a function (which they typically are).
Reduce whitespace in Yiqun

Eliminate excess whitespace to make the code easier to follow, delete
outdated comments and expand on others.