Improve error handling when agent fails on startup.

* The error was swallowed by the agency agent of failing agent, thus
the Host Agent had no way of knowing that there is no point in running
the proposal protocol. Fix that.
* Use error.handle_failure() helper to format the error message nicely.
* Remove layers of delegation. StartAgent task now uses IAgency interface
directly.
Fix parsing port option of standalone db script.
Standalone agent notifies the master agency about the reason for failing
when the exception is raised from initiate_agent().
Handle better import errors triggered by missing modules references
from dynamically loaded applications.
Merge branch 'release-0.26.x'
Don't push notifications about the persitent alerts before an agent
claims responsibility for them.
Fix failing test.
Format better message about test failing because of wait_for() call timeing out.
Fixes in the algorithm merging logs of the concurrent document updates.
Log a reason for webserver responding with 406 NOT ACCEPTABLE.
Refactor QueryViews to allow using class types for the field definitions.

* This allows extending the concept in a clean way.
* Use zope adapter to lookup a view controller used for looking up the result
for a specific query. Its responsible for generating view keys and parsing
results.
Fix problems with reversed view order and key ranges in emu database.
Working example of a version field of the query.

* Simplyified the view definition. reduce() function ended up not being used.
* Integration test checking that the results play out well.
Query can optionaly set the attributes on the resulting docs. The value is
taken from the view index.
Go back to keeping the list of defined fields of the view.

Turns out its important to know it, because the first field is used for
full range query if no condition is defined.
Simplify specifying a view controller to be used for the whole view
instead of each field seperately.
Factor out of the testcase the code to create a version field in a query.
Expose include_value option on the level of database query models.
Fix failing test using private interface.
Bring back the code cleaning up the leading decorator of the object
which code we want to attach to a query view. The inner decorators are
preserved.