Explicit dependency from web/geoserver on geoserver ows module.

Dependencies with scope 'provided' are not transitive. So code with a compile
time dependency (such as the web/geoserver) must explicitly declare it.
Merge pull request #572 from jdeolive/geoserver-ows-dep

Explicit dependency from web/geoserver on geoserver ows module.
Added dependency management for spring-expression.

spring-expression is transitive through ows, which is transitive through
spring-security, which depends on a version different than what geoserver
depends no. Because the geoserver dependencies are provided we don't inherit
the dependency management that deals with this issue.