mitosis:datagrok add layer select, more layouts (#3835)

mitosis:datagrok add layer select, more layouts (#3835)

* mitosis:datagrok: fix typo'd inconsistent brace arrangement

(thank you @cari66ean)

* mitosis:datagrok: add makefile argument MITOSIS_DATAGROK_SLOWUART

* mitosis:datagrok: return backspace to opposite space, use TT(), more

- move backspace back to its position opposite space
- move del to red+backspace
- move tab back to tap-leftshift
- move printscreen/scrolllock/pause to blue+left pinky column
- use TT() instead of MO() to stick a layer on if wanted
- indentation that my text editor wants
- default to no audio; i can enable it at compile time.

* mitosis:datagrok: modularize features, add default layer rotator key

* mitosis: add MITOSIS_DATAGROK_BOTTOMSPACE makefile argument

* mitosis:datagrok: README improvements; document new features

* mitosis:datagrok: dot. not "number pad dot." in numbers layer

* mitosis:datagrok remove unnecessary _user audio code

* mitosis:datagrok: return to MO() for red/blue, keep TT() for purple

in this way, the LED still updates quickly when red or blue is pressed,
but we can still lock the purple layer on for 10-key numpad operation
with red+tapping blue.

* mitosis:datagrok: add colemak and dvorak default layers

* mitosis:datagrok update readme re: available default layouts

* mitosis: remove unneeded code that was overriding led_set_user

also, add some comments

* mitosis:datagrok: updated led setting code for new layers

also, place into led_set_user where it belongs, not matrix_scan_user.

* mitosis:datagrok: update LEDs when setting the default layer

maybe this should go into default_layer_set?

* mitosis:datagrok update readme with new imgur links + other improvements

* mitosis:datagrok fix typo in image urls

* mitosis:datagrok remove useless #include (ty @drashna)

* mitosis:datagrok undo unnecessary change to quantum/quantum.h

i can put the extern float definition in my own keymap code. (ty @drashna)

* mitosis:datagrok move customized layout to my keymap

no need to modify keyboard-level mitosis.h. (ty @drashna)

* mitosis:datagrok update comment describing my led indicator logic

* datagrok:mitosis update readme to document LED indicator.