Support the creation of custom themes: let Git ignore
the theme if it is named "custom". This way the admin may keep
the jirafau git repo and force an update without conflicts.
Let the admin overwrite the content of the
"Terms of Service" page by copying the original ToS
template and creating a local file (same procedure as
for the configuration). This file is not versionized.
Note: This is a breaking change, since the existing
tos textfile is moved. This should be mentioned
in the update comments.
* ToS text file changed → move file from "/tos_text.php"
to "/lib/tos.local.txt" and remove all HTML und PHP Tags,
leaving a regular text file.
Refs #95
