Issue-144 Allow custom email content

Configuration parameter for custom email template.
Loading of alternate template path.
De-static'ized the filename and content properties of the
VelocityEmailHelper to reflect their dependence on a SeyrenConfig only
available on instantiation.  Further de-static'ized the private method
that performed the one-time content initialization.
Added test locking down default.
Added stub test template for loading verification.
Added test that exercises alternatively configured test template.
Updated documentation.
Fix up documentation.
Arbitrary check search by fields and corresponding regular expression.

Modification of checks resource parameters to add fields and regexes.

Added acceptance tests demonstrating, documenting and enforcing usage of check search API.

An example URL is localhost:8080/api/checks?fields=name&patterns=test&fields=description&patterns=test.*description.*
Merge pull request #206 from petems/rebased_email_template

Rebased email template