add ignore list

#### Environment info
* OS: Windows
* App Version : 1.7

#### feature request
Add ignore list~
My Gist is not all of the code snippet. some config file in the Gist. like Atom sync setting files. they are add a lot of worry language tags in my Lepton.

So Can you add ignore list ?

I think ignorelist is a special and unique title in Gist，can help Lepton ignore himself in content.
the ignorelist content is gist id. and have a page in Lepton setting to CRUD this ignorelist.