Add options to open data files by name and to specify data file path

[paulmking]

Is your feature request related to a problem? Please describe.
You can not analyze a particular file by name or absolute/relative path; data files will be searched for by run number, and the search paths are the current working directory and the directory specified by $QW_DATA.

Describe the solution you'd like
I would like to have an option to analyze a particular file by name, instead of just by run number.

I would also like to be able to specify the data directory using a option, instead of using the environment variable.

Both of these would require changes in how QwEventBuffer finds the filename.

[paulmking]

The data directory part of this issue was resolved in develop by pull request #112.