Fix duplicate class issue with generated metadata file

[vinaygaba]

Since the metadata file was simply taking the substring after the last '.' from the package name, it would cause issues if two different modules shared a common substring in their package names. Consider the following two modules -

module 1: com.jll.jet.qraccess.view
module 2: com.jll.jet.hid.view

If both were setup to use Showkase, Showkase would generate the following two files

module 1: ShowkaseMetadataView
module 2: ShowkaseMetadataView

In addition, both these files are added to a fixed package location - com.airbnb.android.showkase

Thus, it would result in duplicate classes.

With the new changes, the entire package name is taken into account. This would help in avoiding this issue.

#198

@airbnb/showkase-maintainers