Speedup CI build by using target platform instead of p2 repositories

[dvojtise]

The build is rather long (mainly due to dependency resolution and downloading) According to https://wiki.eclipse.org/Tycho/Target_Platform

using target platform should speed up the build.

We should try to try to define these platform and remove all P2 repositories in the pom.xml

The only point to verify is : does the target file need regular maintenance to update version of required feature or can we define a simple definition that upgrade easily when a new release of eclipse is done ?