Support single-file Vue components in Web IDE

It looks like single-file Vue components are not supported by the Web IDE:

Screen_Shot_2018-06-17_at_21.48.30

This is same file in the file viewer:

Screen_Shot_2018-06-17_at_21.48.55

In order to use the Web IDE for frontend development of GitLab itself, support for single-file Vue components is essential.