Rename existing Start Python REPL to Terminal REPL

[anthonykim1]

Now with experimental setting for native Python REPL using notebook style UI, we should rename existing REPL to be called as Terminal REPL to reduce confusion.

[anthonykim1]

Verification step:

1. Please download the latest pre-release version of Python extension
2. Use command palette (cmd/ctrl + shift + p) and type 'repl'
3. Observe you see Start... Terminal REPL.. instead of Start... REPL..