Fix for MTOMCAT-177 - tomcat7:deploy ignores proxy settings

AbstractCatalinaMojo provides TomcatManager with proxy configuration from settings.xml

Note - I've added a MavenSession component to AbstractCatalinaMojo - it would probably be possible to use wagonManager.getProxy(url.getProtocol()) as done here: 

https://code.google.com/p/maven-external-dependency-plugin/issues/detail?id=15 

...I'm not sure if that would be best practice, but it seems to be deprecated: 

http://maven.apache.org/ref/3.0.5/maven-compat/apidocs/org/apache/maven/artifact/manager/WagonManager.html
@nalbion, according to Maven docs, `getActiveProxy()` returns **the first** active configured proxy.
This is nice, but it returns the proxy **regardless of its protocol**.

So, let's say, if I have two configured active proxies (the first http and the second https), the plugin tries to use the http proxy for my https host, which results in a NullPointerException.

It's an edge case, but I think that we should choose the proxy depending on the host URL.