float_node: return MAXDOUBLE if min or max is not set.

It's then consistent with the function return type.
tool: fix IntReg display and don't display min/max if they are no specified.
enumeration: set value_type to G_TYPE_STRING.
boolean: return G_TYPE_BOOLEAN as value_type.
tests: test arv_gc_feature_get_value_type.
gst: add a property for access to the underlying ArvCamera object.

It allows to manipulate device parameters during runtime (like gain or
exposure).
camera: try to automatically handle AcquisitionFrameRate/Abs

Like what is done for ExposureTime.
str: implement an illegal characters stripping function.
gv_interface: strip control characters from device id.
doc: minor fixes.