Represents a Map from String to
T where the key's case is not taken into account when looking for it, but
remembered when the key set is retrieved from the map.
The backing map used will be an instance of the given class passed to the constructor. This allows to make case
insensitive different kinds of Map implementations, particularly a ConcurrentHashMap, used to achieve high concurrence.
When a key/value pair is put in the map the key case is remembered so when the key set or the entry set is retrieved
the correct case is returned. This is useful to store, for example, camel case keys. However, two keys that only
differ in their case will be assumed to be the same key and only one value (the last) will be kept.
Note: as this map uses a provided class to create the backing map, key rewrite is not ensured. It is possible that
when redefining a value associated to a key, the key case won't be overwritten and the already existing key case
will remains in the key set and entry set.