Fixes for catalog handling and time parsing

[MJWeberg]

Some minor bugfixes and quality-of-life improvements:

• Improved searching and handling of the EIS as-run catalog
  • Inverted default search pattern (new order: input_dir -> current dir -> home -> SSW)
  • Will also check for write permissions, which are needed for updating the catalog and adding an extra search index
• Improved reliability and flexibility of time format parsing used in the eis_catalog GUI and eispac.db.EISAsRun
  • Can now input a relative "end date" that specifies the number of days before or after the start date
  • Added convenience strings of "start" or "launch" for the first date in the catalog and "now", "today", or "end" for the current date.
• Ensured that the list of templates returned by eispac.match_templates() is properly sorted alphabetically on all operating systems