[CompStrm Wiki] update command environment

[BiLaf <Bi...@Ro...>]

I've now updated CmdEvaluator to provide a proper execution environment
for update commands. This includes establishing single-writer, a
transactional environment, and passing DException messages to the user via
the default display.

Did a bit of reorganizing--all query commands are now in the queries
package. And I've also created an update package for update commands.

A new class, AgileWiki.ark.Validate, has been set up for validating common
data types. I've added only one method todate, userGroup, a static method
for validating what could be either a user or group name.

My intent (I just ran out of time at lunch) is to implement the restrict
command. That way there is at least one command which updates the
database. (So far, all such updates have been handled by evaluators, not
commands. But I expect that there will be a LOT of simple commands. So its
good to have a sample update command.)

Bill