LP#1833080: have eg-bool recognize IDL bool string values

LP#1833080: have eg-bool recognize IDL bool string values

This patch updates eg-bool so that it can format both
true Boolean and IDL bool string values (i.e., 't' or 'f'). Prior
to this patch, IDL bool values would always be rendered as 'Yes'.

This patch relaxes the type restriction on the value setter
and getter; unfortunately, there's no way to overload the
setter or making it accept (say) boolean|string.A

This patch also supplies some unit sets.

To test
-------
[1] View an Angular grid that has Boolean fields. The Copy
    Status server admin page is a good one.
[2] Note that the boolean values are all rendered as "Yes".
[3] Apply the patch and repeat step 1. This time, false
    values should be displayed as "No".
[4] Verify that 'npm run test' for the Angular app passes.

Sponsored-by: PaILS
Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>