audiobasesrc: Add FIXME for times in NSECONDS

Timebase is in nanoseconds pretty much everywhere else
audiobasesrc: Break some too long lines
audiobase*: Drop trailing withespaces
audiobasesrc: Retarget FIXME to 2.0

Properly fixing this one would break API.
audiobasesrc: Bunch of cosmetic/grammar fixes
audio/video-info: Initialize the complete struct to 0 in the beginning

Instead of only initializing some parts in some code paths. Also
makes it easier to use the reserved bits of the structs later.

https://bugzilla.gnome.org/show_bug.cgi?id=720810
audio/video-info: Properly initialize the info structures in set_format()

And don't assume in other code that set_format() preserves any fields at
all. These assumptions were already made here for fields that were changed
by set_format().
playback: add ANY caps features to default audio/video raw caps

Allows elements using audio/video caps features to be used by playbin.