Correct dependency version of aspectjweaver used for spring-aop

The current used spring version is configured in the project pom (4.1.4.RELEASE) but the aspectj(weaver) version, as used/needed for spring-aop is configured in the hst pom.xml.
As a result, these are now out-of-sync: currently used aspectjweaver version 1.6.9 is not Java8 compatible, instead version 1.8.4 must be used.

I'll fix this by adding to the project pom:

  <aspectjweaver.version>1.8.4</aspectjweaver.version> <!-- should be synchronized with dependency of spring-aop -->

and remove the aspect.version property from the hst pom.