Update clone handler template

[mpacer]

As part of the fs cloning handler, it requires changing how the clone.html template works. This makes it easier to construct a template that works for both handlers.

Main two changes are to move common behaviour to the backend, specifically:

1. creating the post model
2. creating the description of the source file

[codecov[bot]]

Codecov Report

Merging #156 into master will increase coverage by 0.04%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #156      +/-   ##
==========================================
+ Coverage   79.39%   79.43%   +0.04%     
==========================================
  Files          10       10              
  Lines         427      428       +1     
==========================================
+ Hits          339      340       +1     
  Misses         88       88

[mpacer]

@chyzzqo2 does this look ok to you?