templater: store revisions as ints so min/max won't compare them as strings
Because a template value has no explicit type (like ancient PHP), ifcontains()
has to coerce the type of the needle. Before, it was always converted to a
string, which meant any container type should be a list/dict of strings.
This no longer works since we've introduced min/max functions.
In order to work around the untyped nature of templater, this patch adds
a type specifier to hybrid dict/list. It isn't named as "valuetype" since
the _hybrid class can also wrap a dict.