Makes the TP values into properties for use in target-platform pom

* Disable the attachment of the teiid-designer.target platform since its
  identical to the target platform configuration now downloaded via mvn

* The generation of the teiid-designer.target can remain since devs can use
  this for specifying their TP in eclipse IDE

* Adds a README for developers to understand how to create a .target file
  for use with eclipse IDE
Stops the ant-contrib library being downloaded to invalid locations

* On occasion the ant-contrib library can get downloaded to
  ${ant.library.dir} when this property has no value. Avoid this by
  just checking on the value of this property prior to downloading
Generate target-platform files with version appended to them

* Having a teiid-designer-${td.tpc.version}.target allows multiple targets
  to be generated locally and means that TPs in eclipse can be switched
  rather than having to be re-downloaded, reducing the effort in changing
  branches and TPs
TEIIDDES-2352: Save the jdbc password token to xml

* The jdbc password token is not being saved to the xml file hence the
  password is not found and reverting to the default upon reloading

* Completes the cycle by saving the jdbc password token in the same manner
  as the admin password