Improvements to assemble_synApps.sh

[kmpeters]

1. Allow module versions to be specified in a separate file or multiple files, passed as arguments to the script.
2. Allow a name other than "synApps" to be used for the top-level directory (defined by the SYNAPPS_DIR variable).

These changes are backwards compatible; calling assemble_synApps.sh with the 'full' argument or no arguments will behave as it did in the past.

[kmpeters]

For example, if you want a synApps-alive directory that only contains the alive module, you could create a file named alive with these contents:

EPICS_BASE=/APSshare/epics/base-3.15.6

SYNAPPS_DIR=synApps-alive

SUPPORT=R6-1
CONFIGURE=R6-1
UTILS=R6-1
DOCUMENTATION=R6-1

ALIVE=R1-1-1

And then call the assemble script:

$ assemble_synApps.sh alive