Make the extension download and/or run ucm

[jneira]

Hi, it is a pretty usual feture of langauga extension download and run the tool needed to have a working and running lsp server.
It helps beginners start and check faster the language but it adds more complexity to the extension.
Incremental features could be:

1.- Execute UCM in the current workspace folder if the executable is in the global $PATH
2.- Add a configuration property to let users set the path to the ucm executable.
3.- Optionally download ucm if it is not already installed

Thanks in advance

[ChrisPenner]

Looks like 1 & 2 are done!

Remaining is optionally downloading ucm, which is platform specific; but would likely be easy enough to implement for any platforms that we provide a binary for.