Ensure that JPA 2.0 is available and actually used

o.e.s.jpa and o.e.s.api have a dependency to JPA 2.0, i.e.
TypedQuery, which is not available in earlier JPA releases.
If the javax.persistence package is available as JPA 1.0 and
JPA 2.0 Tycho tends to take JPA 1.0, which breaks the build.

Added jpa:2.0 modifiers to the javax.persistence manifest entries
of the mentioned bundles.

Change-Id: If892a46b1bcd30e9c17a0d2733319af02224ad06
Signed-off-by: Michael Ochmann <michael.ochmann@sap.com>
Build standalone product only if build-product profile active

Build of the the standalone product and the necessary
orbit/jetty/eclipse features is now performed only, if Tychco is
started with the profile parameter -Pbuild-product.
By default, only a p2 repository with the Skalli bundles,
source bundles and testutils bundle is produced.

This speeds up the build considerably and simplifies consumption
of Skalli for use in other web containers.

Change-Id: Ia47a8703a4b6e8d4940fa81a7e13f7fa4780da2c
Signed-off-by: Michael Ochmann <michael.ochmann@sap.com>