Revise reports based on Mike Walters' examples

Mike Walters did some reworking of the reports locally and I think some of the stuff he did may generalize to making our reports more clear and useful.

• add a command line option to turn on variables missing that were specified in the config file being an error (done in #17 (closed) )
• add a line to the comparison results table for each variable that was requested (in the config or on the command line as appropriate) but could not be found or compared for whatever reason (only when '--warnmissingvars' is used on the command line)
• add a summary line for the compared variables with how many passed and failed (+ errored)
• a table based display of the variable comparison details in the "Compared Variables" section

- [ ] next/back/up links in the header to make quickly navigating the whole report easy

• on the variable page, note whether or not that variable passed comparison

Here are some example reports from Mike for reference:

index__1_.html index__2_.html index.html

Mike has also requested the ability to have Glance use configurable custom report templates with the same input data as my regular templates. I'm not doing that in this issue, but this is a note to myself to reassess how difficult that's going to be once I've done the other stuff here.

Note to self: I added a '--warnmissingvars' command line option to warn about missing variables on #17 (closed) but I still need to add the changes to put that info in the main report page on this ticket.

Edit: I've decided not to do the next/back/up links, since a batch of reports can more easily be navigated from the new summary page.