Support R session requests by hosting a tcp server

[Tal500]

Closes #1359 Fixes #1391

Features:

• [X] TCP R connection
• [X] Visual&logical attaching/detaching from the TCP server (since 4bae0a7cad439db1e9b221601192967aa9a8cc09)
• [X] Correct loading init.R after R session init (and connect by it on pressing the status icon when opening a new terminal): Connect on already active R session via source("~/.vscode-R/init_late.R"); .vsc.attach(host="YOUR_HOST", port = YOUR_PORT);. (since 873af37ec2fceaee2c144aa62be72bd71562078e)
• [X] Namespaces and global environment view
• [X] View data
• [X] Plots (since 0d7f44f1554c433a6d13d16e0d4e4f532d43a5ff)
• [X] Man pages
• [X] Web server is working
• [X] Make TCP listening configurable
• [X] Add .vsc.detach to API
• [X] Default viewers when not detached (since 860c8d5856e519282b450d70faf1fa8de8c2c5d2)
• [X] Detach button in VSCode UI (since b45db8d191bb995b5ef8c02410ba38a0ef2d531e)
• [X] Webview display of file path as one that goes trough TCP and not by local path - including the HTML "lib" dir dependencies, when detected. (since db53c609e1a6866840051d1f180dca5c5502ae48)

Not Planned:

• Portforwarding of 127.0.0.1 of URL based webview.