Centralised beep code to lcd_buzz().
From gcode_M300() and lcd_quick_feedback().

Enforced max. duration for M300 to 5 seconds.

Corrected description in 'Configuration.h'

LCD_FEEDBACK_FREQUENCY_HZ 0 gives now a silent delay of
LCD_FEEDBACK_FREQUENCY_DURATION_MS.

- Replace “Mendel” with “RepRap”

Don’t set CUSTOM_M_CODE_SET_Z_PROBE_OFFSET if there’s no Z probe

make it unconditional
remove all definitions in the 'Configuration.h's
remove form 'Conditionals.h'

- Address issue #1669
- Remove the TOPO_ORIGIN configuration setting

- `Conditionals.h` is included twice, setting LCD values the first time

- Add `Conditionals.h` with calculated configuration values
- Add `SanityCheck.h` with checks for configuration errors
- Remove equivalent code from all configurations
- Move error checks from some sources to `SanityCheck.h` also
- Fix initialization of count_direction in stepper.cpp

- Addressing issue #1608

- Also update base configs

- Do field grouping
- Tweak configurations for better grouping

Slightly better layout for wide screens.

- Auto-detect “switchable” items where possible
- Handle switchable multi-value fields
- Add standard sections to config form
- Add section markers to configurations
- Add value options to configurations
- Remove and re-add fields for loaded configs
- Preserve sections across configs
- Preserve non-added fields
- Style added fields wider & newline by default

- Fetch code now handles github, local, or http: access
- Download button creates a time-stamped inline download
- More complete error messages
- Show warnings when approaching the hourly fetch quota (limit
reloading!)
- Added my test domain (where the _htaccess is deployed)
- `_htaccess` file added to set Access-Control-Allow-Origin “*”
- Marlin logo with css
- Limit selectable areas to avoid annoying selections
- Messages now persist until dismissed
- Default repo for files set to thinkyhead, ‘marlin_configurator’ branch
- Cosmetic changes

Browsers may not want to load files outside the folder, but they may be
okay with these relative references within the folder.

This reverts commit 935ee968a7.

Still not fine tuned but working.