[feature] Implementation of flash erase in stlink-gui

[rkompass]

Thanks for this nice project.
I found it easy to install (it's already on Ubuntu and Manjaro).

Now trying to use the GUI I miss the button to erase the flash.
Is this intended?

Would be nice to have it too.

Thanks

• I made serious effort to avoid creating duplicate or nearly similar issue

In order to allow developers to isolate and target your respective issue, please take some time to select the check boxes below and fill out each of the following items appropriate to your specific request.

• Programmer/board type: [STLINK /V2,]
• Operating system and version: [Linux, Manjaro]
• stlink tools version and/or git commit hash: [1.8.0-2] (latest on Manjaro)
• stlink commandline tool name: [STLink GUI]
• Target chip (and board, if applicable): [STM32F405RG] (Pyboard 1.1)

[Nightwalker-87]

@rcubee has contributed to this issue.