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.