Make Reporter::SingleFile abstract
Add report_path accessor to Reporter::SingleFile
SoftwareResultify CombineReport command
Remove CombineSnvIndelReports command
Make call signature more specific
Add explicit is_optional to input property

Some places in our codebase accept that is_optional is implied by default
declarations, but not all places do. Perhaps this should be set for us
by UR if we supply a default declaration.
Add user and process_id inputs to CombineReports
Make inputs into constants

This makes it easier to compose these dags later.
Add interface to determine combine parameters

This will be used by CreateCombinedReports to determine if we should try
to combine reports or not and with what parameters.
Add CreateCombinedReports Command
Relax restriction on declaring constants again
Redeclare labels

This will make it possible to look up any specific SR we create.
Rename Reporter to Report everywhere
Rename Combine to Merge
Rename MergedReportsResult to MergedReport
Move MergeReports into Framework
Add Test::MergedReport
Change model input to build input for summary commands
Command can still use model interface
Change AlignmentStatsSummary to a command-sr pair

Change coverage stats summary to cmd-sr pair