Unbundle EVIO

To build the analyzer, we now need EVIO headers and shared libraries
installed in EVIO_INCDIR and EVIO_LIBDIR, respectively. To run the
analyzer, EVIO_LIBDIR needs to be in LD_LIBRARY_PATH.

Building standalone decoder executables and library hasn't been
tested yet. The standalones should probably also be split from the
decoder library build.

There are remaining issues about including evio.h. Ideally, the
analyzer should hide the low-level EVIO implementation and provide
its own, standalone API. This is currently not the case for
THaEvData and THaCodaData.