Added support for Samsung Galaxy J7 Prime (#209)

Added support for the Samsung Galaxy J7 Prime.

@linhcentrio if you are comfortable with it, please test this config.

resolves #173

Author: tsterbak

README.md

@@ -72,6 +72,7 @@ Help to improve the tool by reporting any issues you might face.
 Vendor | Device Name | CodeName | Models | Status
 ---|---|---|---|---
 Samsung | Galaxy J7 2015 | j7elte | | tested
+Samsung | Galaxy J7 Prime | on7xelte | | untested
 Samsung | Galaxy A3 2017 | a3y17lte | SM-A320FL | tested
 Samsung | Galaxy A5 2016 | [a5xelte](https://wiki.lineageos.org/devices/a5xelte) | SM-A510F | tested
 Samsung | Galaxy A5 2017 | [a5y17lte](https://wiki.lineageos.org/devices/a5y17lte) | | tested

openandroidinstaller/assets/configs/on7xelte.yaml

@@ -0,0 +1,28 @@
+metadata:
+  maintainer: MagicLike
+  device_name: Samsung Galaxy J7 Prime
+  is_ab_device: false
+  device_code: on7xelte 
+  supported_device_codes:
+    - on7xelte
+  untested: true
+steps:
+  unlock_bootloader:
+  boot_recovery:
+    - type: call_button
+      content: >
+        As a first step, you need to boot into the bootloader. A bootloader is the piece of software, 
+        that tells your phone how to start and run an operating system (like Android). Your device should be turned on. 
+        Then press 'Confirm and run' to reboot into the bootloader. Continue once it's done.
+      command: adb_reboot_download
+    - type: call_button
+      content: >
+        In this step, you need to flash a custom recovery on your device.
+        Press 'Confirm and run' to start the process. Confirm afterwards to continue.
+      command: heimdall_flash_recovery
+    - type: confirm_button
+      img: samsung-buttons.png
+      content: >
+        Unplug the USB cable from your device. Then manually reboot into recovery by pressing the *Volume Down* + *Power buttons* for 8~10 seconds 
+        until the screen turns black & release the buttons immediately when it does, then boot to recovery with the device powered off, 
+        hold *Volume Up* + *Home* + *Power button*.