add ignore project capabilities

[MSBarbieri]

i needed a way to ignore two projects in my workspaces.
one specific by the dirName and another by a subdir.

info: i'm not an english speaker, so please check if i write something wrong

[GnikDroy]

I took a cursory look at the PR. And everything looks great. Well done.

Although, I have a few questions since this breaks the current API (workspaces.json format is not same).

Instead of ignore_patterns and ignore_dirs, perhaps we can let users configure a filter function. This will allow more power at the cost of slightly difficult configuration. Additionally, this won't break the current API. But the cost is we can't specify ignore_patterns and ignore_dirs dynamically through the json file. What are your thoughts on this?