Adding file deregister tool + extrapolating code

This solves some TODOs by moving shared code out into
`_blackbox_common.sh`.

New VCS commands were added, `vcs_ignore` and `vcs_notice` (the
opposite of ignore).

Made some utility functions

* `remove_filename_from_cryptlist` - The opposite of `add_file_to_cryptlist`
* `remove_line` - Removes a single line from a text file

bin/blackbox_register_new_file

@@ -11,7 +11,6 @@
 set -e
 blackbox_home=$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )
 source "${blackbox_home}/_blackbox_common.sh"
-_determine_vcs_base_and_type
 
 unencrypted_file=$(get_unencrypted_filename "$1")
 encrypted_file=$(get_encrypted_filename "$1")
@@ -37,7 +36,6 @@ echo "========== CREATED: ${encrypted_file}"
 echo "========== UPDATING REPO:"
 shred_file "$unencrypted_file"
 
-VCSCMD=$(which_vcs)
 if "$SECRETSEXPOSED" ; then
   vcs_remove "$unencrypted_file"
   vcs_add "$encrypted_file"
@@ -46,23 +44,10 @@ else
   COMMIT_FILES=("$BB_FILES" "$encrypted_file")
 fi
 
-# TODO(tlim): This should be moved to _blackbox_common.sh in a
-# VCS-independent way.
-IGNOREFILE="${REPOBASE}/.${VCS_TYPE}ignore"
-if [[ $VCS_TYPE = 'git' ]]; then
-  relfile="$(vcs_relative_path "$unencrypted_file")"
-  relfileb="${relfile/\$\//}"
-  ignored_file="$(echo "${relfileb}" |  sed 's/\([\*\?]\)/\\\1/g' | sed 's/^\([!#]\)/\\\1/')"
-  if ! grep -Fsx >/dev/null "$ignored_file" "$IGNOREFILE"; then
-    echo "$ignored_file" >>"$IGNOREFILE"
-    COMMIT_FILES+=("$IGNOREFILE")
-  fi
-  vcs_add "$IGNOREFILE"
-fi
-
+vcs_ignore "$unencrypted_file"
 echo 'NOTE: "already tracked!" messages are safe to ignore.'
 vcs_add "$BB_FILES" "$encrypted_file"
 vcs_commit "registered in blackbox: ${unencrypted_file}" "${COMMIT_FILES[@]}"
 echo "========== UPDATING VCS: DONE"
 echo "Local repo updated.  Please push when ready."
-echo "    $VCSCMD push"
+echo "    $(which_vcs) push"