avoid 'integratedTerminal' and 'externalTerminal'. Rather use 'terminal'

[aeschli]

For #6654.
Right now the settings are called
"integratedTerminal.shell.linux": "/bin/bash"
"externalTerminal.windowsExec": "cmd",

If you look at other settings, we avoid camelcase in the first segment.
I'd suggest to group everything under terminal.

-> One setting that chooses which terminal type to use (e.g. when invoking 'Open in terminal').
'external', 'integrated'. IMO intergrated should be the default.
-> terminal.external.windowExec ...
-> terminal.integrated.shell

[Tyriar]

I like it

[Tyriar]

8c1dff7

[Tyriar]

I think I changed all the important places where I mentioned it in:

• https://github.com/Microsoft/vscode-docs/blob/vnext/release-notes/latest.md
• Request feature "Integrated terminal" #143 (comment)