Library for reentant code

It would be desirable to have p348reco, at least partially, as a library. A number of issues can be addressed at the same time:

• Build time for numerous executables in p348reco/ dir had become a nuisance because of the number of #included headers -- from STL, ROOT, GenFit, etc. Even small change in the reco code require ~2min of compiling a single .exe. Library would sufficently decrease this time
• Linkage with external projects. Putting implementation in header file results in a conflict if the header file is included into more than one linkage unit. That strictly constrains user code to a single-file unstructured projects.
• Better structuring of the entire project. Currently, conddb.h is of ~4k lines of code, p348reco.h is of ~2k and despite of intended design it is sometimes hard to predict responsibility of particular code.

Since our Makefile now looks rather like a package manager, with GenFit and TrackingTools patching and installation routines, it seems to become feasible in general to benefit from technology of shared libraries.

I would propose to discuss some pieces that can be packed up into library, from the point of view:

• maturity
• reentrant usage
• expensive build time.

First candidates for that:

• Shower profile reconstruction
• APV detector clustering
• Calibrations (including SDC)

I can implement this shortly, but would like to collect opinions first, since the whole collaboration could benefit from such refactoring.