Added feature wherein the .gittress contains important information regarding subtrees

The .gittress file contains the following -
1. URL for the subtree that is merged to the parent project
2. Name of the subtree repository on the local folder and specified
using --prefix option.
3. subtreeCommit field that provides the latest commit information for
the subtree that is merged in and currentCommit field contains commit
information for the commit that gets generated due to the merge of the
two branches.