Add option to use custome keymap

[Zkffkah]

I switch between mac & windows regularly too like #67, but I want to use mac keybindings in windows.
So in IDEA windows, I have my own solution . I use my own keymap in IDEA windows and switch the alt windows and ctrl key to simulate the macOs keymap. I was wondering if there're any ways for me to apply my own keymap on this awesome plugin.
Thanks

[lmserrano]

I also would make use of this feature. I switch a lot between both platforms and it would be great if it could be possible to:

• Have an easy to tell the plugin if we want it to set the Windows or the Mac defaults (regardless of the platform in which we are running VS Code on)
• Use custom keymappings

[kasecato]

Related issues: #67