v1.4.1 : add check on existence of config script

Below, I've copied the manually-written sections of the v1.4.0 release for reference. Look at that release for the detailed list of what was changed relative to the last minor release.

💥 Breaking Changes (relative to v1.3.6)

• While #77 technically is a breaking change, no processor on ldmx-sw:trunk uses any of the must* hints. The behavior of should* hints have stayed the same and so I am not making a big deal out of it.
• #73 removes the Framework/EventDef.h header and so a few modules will need to be cleaned in order to remove any inclusions of that header. In addition, since the event dictionary is being generated in a different way, users should be encouraged to do a completely clean rebuild so conflicts can be avoided. This means they must not only rm -r build but also cd Framework; git clean -xxfd to remove the previously generated files.
• #87 changed Event::exists to require a full-string match. i.e. if there are two collections MyCollection and MyCollectionBeta, before #87 Event::exists("MyCollection") would fail because two possibilities were found, now it will pass because only MyCollection is found. The documentation points the user to use Event::searchProducts directly if non-full-string-matching is required for a more complex search algorithm.

✨ Highlights (relative to v1.3.6)

• allow for . to exist within a configuration scripts file name (and not just its .py extension) by running the configuration script as a Python script rather than importing it as a module #76
• rework storage control voting decision to actually separate must* and keep* hints into different levels of importance/priority #77
• prevent dumping of TClassInfo errors when closing the program early during processing by making sure to close up any open TFiles #78
• move generated LinkDef file into the build directory so that developers don't need to git clean the Framework module if an event object is changed or added #73
• store number of events started (a.k.a. the number of tries) in the run header for luminosity calculations #81
• performance monitoring of time at various important points in processing #83
• update searchProducts and exists to be more flexible and more understandable #87

What's Changed

• explicitly check if the config is readable before continuing by @tomeichlersmith in #92

Full Changelog: v1.4.0...v1.4.1