Refactor template resolution

Refactor template resolution

Resolve functions in templates by making a copy of the data rather than
modifying the original. This means that e.g. a resource resolving functions
in its own template data does not result in changes to the data held by the
Stack.

This patch also refactors all of the template resolution methods to operate
using a common parsing algorithm to move through the tree.

Finally, the resources have been worked to load data as it is needed,
rather than requiring external code to put them into the correct state
before using them.

Change-Id: I79eafaefc9ced07b652fac7162aa2edbfa7f547a
Signed-off-by: Zane Bitter <zbitter@redhat.com>