FS-7506 FS-7513: set banner with video_banner_text variable set before calling in, NEEDS DOCS params are parsable inside a {} string

duplicated some code from 4943~4953, but that code has it's own problem, it forget to reset *bytes results to
larger frame->datalen could read beyond the buffer, and it also makes stats not accurate. But if we reset *bytes
at that place, then later the switch_vb_put_packet has problem because it depends that *bytes. this patch should
fix the datalen at least buf still leaves duplicated code and inaccurate stats.

FS-7513: round screen size to even numbers to prevent green lines on edge with 1up_top_left+5 and 6x6 layouts

FS-7513: add flag to choose between encoding each frame and using central encoder per codec, add parsing for floor fields and reservation fields in layouts, add param to control bandwidth for consolidated codecs, add  audio-position attr to images in layout to sync with virtual HRTF

FS-7513: refactor conference video muxing to create one distinct encoder per codec used and only create one encoded frame per distinct codec, store current image used by layer on the layer so it is not destroyed before the canvas is written, refactor and rearrange some functions