[Keyboard] Add 7splus keyboard (#10538)

* Add 7splus keyboard.

A 85 keys ANSI Layout split keyboard.
Salicylic-acid3

* Update keyboards/7splus/keymaps/default/keymap.c

Co-authored-by: Drashna Jaelre <drashna@live.com>

* Update keyboards/7splus/keymaps/salicylic/keymap.c

Co-authored-by: Drashna Jaelre <drashna@live.com>

* Update keyboards/7splus/rules.mk

Co-authored-by: Ryan <fauxpark@gmail.com>

* Added VIA keymap and a few updates

Adding a VIA Keymap
Updating the key layout diagram
Copywrite added for salicylic keymap

Co-authored-by: Drashna Jaelre <drashna@live.com>
Co-authored-by: Ryan <fauxpark@gmail.com>

keyboards/7splus/rules.mk

@@ -0,0 +1,24 @@
+# MCU name
+MCU = atmega32u4
+
+# Bootloader selection
+BOOTLOADER = caterina
+
+# Build Options
+#   change yes to no to disable
+#
+BOOTMAGIC_ENABLE = lite     # Virtual DIP switch configuration
+MOUSEKEY_ENABLE = no        # Mouse keys
+EXTRAKEY_ENABLE = yes       # Audio control and System control
+CONSOLE_ENABLE = no         # Console for debug
+COMMAND_ENABLE = yes        # Commands for debug and configuration
+# Do not enable SLEEP_LED_ENABLE. it uses the same timer as BACKLIGHT_ENABLE
+SLEEP_LED_ENABLE = no       # Breathing sleep LED during USB suspend
+# if this doesn't work, see here: https://github.com/tmk/tmk_keyboard/wiki/FAQ#nkro-doesnt-work
+NKRO_ENABLE = no            # USB Nkey Rollover
+BACKLIGHT_ENABLE = no       # Enable keyboard backlight functionality
+RGBLIGHT_ENABLE = yes       # Enable keyboard RGB underglow
+BLUETOOTH_ENABLE = no       # Enable Bluetooth
+AUDIO_ENABLE = no           # Audio output
+
+SPLIT_KEYBOARD = yes