[dev] Hermes timeslice_rate

[Chuck Hagenbuch]

Quoting Duck <duck at obala.net>:

> I tried to go forward with implementing Minerva for Hermes invoices. I see
> that Herems has a field “timeslice_rate” but as I can see this field is used
> anywhere. Has this field any special purpose or can be dropped?

It's referenced once in lib/Driver/sql.php and returned in the  
getHours() data. It doesn't seem to be used much if at all though.  
Seems like the idea is to allow setting a custom rate on any  
timeslice, right? If we drop it, we're enforcing that all work for a  
job type is always going to be the same rate - which brings up issues  
with historical data when job type rates are edited.

I don't feel strongly about the rate-per-slice, but historical changes  
probably need to be handled somehow.

-chuck