UFS file editor GUI_FILE_EDIT

[barbudor]

Description:

Let's edit autoexec.bat and all Berry files on the target
Optionally enabled with #define GUI_EDIT_FILE

Tested both on ESP8266 with 4MB linker file and ESP32 with default 64kB FFS
Tested only on root folder of FFS
Not tested yet with big files (no size control implemented)
Not tested with SDCARD and folders (testers welcomed as I don't have a board with SDCARD slot)

Note: I also changed the href to file download & delete to be relative instead of absolute with IP address. That's nicer when you open the Web GUI from a hostname instead of an IP address and also wouldn't work when accessing a device through a ssh tunnel (it's local IP address is not the one you are using to access it).

Checklist:

• The pull request is done against the latest development branch
• Only relevant files were touched
• Only one feature/fix was added per PR and the code change compiles without warnings
• The code change is tested and works on Tasmota core ESP8266 V.2.7.4.9
• The code change is tested and works with core ESP32 V.1.0.6
• I accept the CLA.

NOTE: The code change must pass CI tests. Your PR cannot be merged unless tests pass