Import trusted GPG keys for git-crypt

Initialized git-crypt for the repository with `git-crypt init`.

Added GPG keys of all core team members by running the
`git-crypt add-gpg-user --trusted --no-commit <ID>` command where
`--no-commit` flag prevents automatic commit of generated files while
`--trusted` assumes the GPG user IDs are trusted.

Epic GH-33
Depends on GH-35 GH-49
Resolves GH-48

.git-crypt/.gitattributes

@@ -0,0 +1,4 @@
+# Do not edit this file.  To specify the files to encrypt, create your own
+# .gitattributes file in the directory where your files are.
+* !filter !diff
+*.gpg binary