Use more logical Boards menu placement for Uno Mini

Arduino has added a new board to the AVR-based line: the Uno Mini. The Uno Mini has its own board definition in this
platform, which produces a dedicated item in the **Tools > Board** menu of the Arduino IDE.

The classic Arduino IDE arranges the Boards menu for each platform according to the order of occurrence of the board
definition in the platform's boards.txt configuration file. The previous placement of the Uno Mini board definition
resulted in the board appearing at the end of the menu, along with retired and 3rd party boards.

The new placement will cause it to be shown alongside the related Arduino Uno and in a position befitting the latest
official AVR board.

boards.txt

@@ -103,6 +103,39 @@ uno.build.variant=standard
 
 ##############################################################
 
+unomini.name=Arduino Uno Mini
+
+unomini.vid.0=0x2341
+unomini.pid.0=0x0062
+unomini.upload_port.0.vid=0x2341
+unomini.upload_port.0.pid=0x0062
+unomini.upload_port.4.board=unomini
+
+unomini.upload.tool=avrdude
+unomini.upload.tool.default=avrdude
+unomini.upload.tool.network=arduino_ota
+unomini.upload.protocol=arduino
+unomini.upload.maximum_size=32256
+unomini.upload.maximum_data_size=2048
+unomini.upload.speed=115200
+
+unomini.bootloader.tool=avrdude
+unomini.bootloader.tool.default=avrdude
+unomini.bootloader.low_fuses=0xFF
+unomini.bootloader.high_fuses=0xDE
+unomini.bootloader.extended_fuses=0xFD
+unomini.bootloader.unlock_bits=0x3F
+unomini.bootloader.lock_bits=0x0F
+unomini.bootloader.file=optiboot/optiboot_atmega328.hex
+
+unomini.build.mcu=atmega328p
+unomini.build.f_cpu=16000000L
+unomini.build.board=AVR_UNO
+unomini.build.core=arduino
+unomini.build.variant=standard
+
+##############################################################
+
 diecimila.name=Arduino Duemilanove or Diecimila
 
 diecimila.upload_port.0.board=diecimila
@@ -1273,36 +1306,3 @@ unowifi.build.esp_ch_uart_br=19200
 unowifi.build.extra_flags=-DESP_CH_UART -DESP_CH_UART_BR={build.esp_ch_uart_br}
 
 ##############################################################
-
-unomini.name=Arduino Uno Mini
-
-unomini.vid.0=0x2341
-unomini.pid.0=0x0062
-unomini.upload_port.0.vid=0x2341
-unomini.upload_port.0.pid=0x0062
-unomini.upload_port.4.board=unomini
-
-unomini.upload.tool=avrdude
-unomini.upload.tool.default=avrdude
-unomini.upload.tool.network=arduino_ota
-unomini.upload.protocol=arduino
-unomini.upload.maximum_size=32256
-unomini.upload.maximum_data_size=2048
-unomini.upload.speed=115200
-
-unomini.bootloader.tool=avrdude
-unomini.bootloader.tool.default=avrdude
-unomini.bootloader.low_fuses=0xFF
-unomini.bootloader.high_fuses=0xDE
-unomini.bootloader.extended_fuses=0xFD
-unomini.bootloader.unlock_bits=0x3F
-unomini.bootloader.lock_bits=0x0F
-unomini.bootloader.file=optiboot/optiboot_atmega328.hex
-
-unomini.build.mcu=atmega328p
-unomini.build.f_cpu=16000000L
-unomini.build.board=AVR_UNO
-unomini.build.core=arduino
-unomini.build.variant=standard
-
-##############################################################