Moved hard coded paths into new config file WEB-INF/agwa.properties

I wanted agwa.properties to be able to contain placeholders so that
property definitions could depend on other already defined properties.
In order to do this I had to use class org.springframework.util.PropertyPlaceholderHelper
which is only available in spring-core > 3. Wayback was using spring-core-2.5.1.jar
so having checked for backwards binary compatibility of spring-core-3.2.3.jar I
dropped it into WEB-INF/lib as a replacement. Then I updated nla-web-archive.js
to include functionality allowing things like the base URL of the AGWA server to
be set via Javascript.
The only Wayback JSP files which required URLs referring back to the AGWA system
were WEB-INF/exception/HTMLError.jsp and WEB-INF/replay/Toolbar.jsp so these
have been modified to use the newly implemented functionality.
Modified configuration system used by agwa-wayback so that agwa.properties is only read once per session. 

The previous incarnation very inefficiently loaded the properties file on every request (it was only a proof of concept).

This includes the following changes:

* In /WEB-INF/exception/HTMLError.jsp and /WEB-INF/replay/Toolbar.jsp session attributes 'agwaBaseUrl' and 'agwaPrefixQueryUrl' are initialised only if session attribute 'agwaPropertiesLoaded' is null. Once the session attributes have been initialised this attribute is set to true;

* Removed spring-core-3.2.3.RELEASE.jar and replaced it with spring-core-3.0.5.RELEASE.jar to match the versions of other Spring Framework JARs;

* Added /WEB-INF/org.springframework.web-3.0.5.RELEASE.jar because

* In wayback.xml changed wayback.urlprefix to http://htx-mpearson:8080/agwa-wayback/wayback/ to match the GIT project name and the default TomCat web-app name
Merge pull request #1 from mpearson-nla/master

Pull changes from mpearson-nla/govau-wayback