Random cleanup and smaller bugfixes

Random cleanup and smaller bugfixes

Use gst_element_klass_set_details_simple(), install properties
with static strings, create pads directly from the static pad
templates, directly put the segment into the instance struct,
use GST_MSECOND instead of numbers.

The PAR is a GstFraction and not a double, use gst_structure_get_fraction().

Simplify setcaps() functions.