Add gap+pulse period distribution to analyzer

[zuckschwerdt]

Adds "Gap+pulse period distribution:" histogram to the analyzer.

Also renames "Pulse period distribution:" to "Pulse+gap period distribution:"
and "Pulse timing distribution:" to "Timing distribution:".

E.g. the following analysis (rtl_433_tests/tests/cardin/01/S466-TX2_01.cu8) shows that leading gaps are used in the transmission:

Analyzing pulses...
Total count:  624,  width: 2145.65 ms		(536412 S)
Pulse width distribution:
 [ 0] count:   25,  width: 6156 us [6140;6220]	(1539 S)
 [ 1] count:  275,  width:  728 us [720;740]	( 182 S)
 [ 2] count:  324,  width: 1408 us [1400;1420]	( 352 S)
Gap width distribution:
 [ 0] count:  275,  width: 1368 us [1352;1384]	( 342 S)
 [ 1] count:  324,  width:  696 us [688;708]	( 174 S)
 [ 2] count:   24,  width: 30448 us [30448;30460]	(7612 S)
Pulse+gap period distribution:
 [ 0] count:   25,  width: 7516 us [7508;7572]	(1879 S)
 [ 1] count:  200,  width: 1428 us [1420;1444]	( 357 S)
 [ 2] count:  175,  width: 2780 us [2776;2788]	( 695 S)
 [ 3] count:  199,  width: 2104 us [2096;2116]	( 526 S)
 [ 4] count:   24,  width: 31864 us [31856;31872]	(7966 S)
Gap+pulse period distribution:
 [ 0] count:    1,  width: 6220 us [6220;6220]	(1555 S)
 [ 1] count:  599,  width: 2104 us [2088;2120]	( 526 S)
 [ 2] count:   24,  width: 36604 us [36592;36616]	(9151 S)
Timing distribution:
 [ 0] count:   25,  width: 6156 us [6140;6220]	(1539 S)
 [ 1] count:  599,  width:  712 us [688;740]	( 178 S)
 [ 2] count:  599,  width: 1392 us [1352;1420]	( 348 S)
 [ 3] count:   24,  width: 30448 us [30448;30460]	(7612 S)
 [ 4] count:    1,  width: 62204 us [62204;62204]	(15551 S)