Added pre/post hook targets to core build.xml

# Warning
# Info
* The following pre/post hook targets now exist in the core build.xml file to allow injecting project specific functionality without the need to override the entire target
    * preUninstall
    * postUninstall
    * preUpdateRequiredPackages
    * postUpdateRequiredPackages
    * preDeploy
    * postDeploy
    * preDeployCI
    * postDeployCI
    * preDeployCIPackageOrg
    * postDeployCIPackageOrg
    * preDeployManaged
    * postDeployManaged
    * preDeployManagedBeta
    * postDeployManagedBeta

# Issues
Fixes #20