Update Bundlor to support explicit Import-Package:

Add a new 'importPackage' variable to the bundlor task allowing the
specification of 'Import-Package:' for the manifest template.

This change is driven by the fact that Bundlor does not automatically
detect arguments to Annotations (e.g. MetricType in @ManagedMetric).
Merge pull request #11 from garyrussell/explicitPackageImport

# By Gary Russell
* explicitPackageImport:
  Update Bundlor to support explicit Import-Package: