[v1] Warning if Bootstrap 3 classes are used

[Herst]

Check for some Bootstrap 3 classes, at least those where I assume that are unlikely to be used for anything else, if they are detected then a new warning with the is id W018 is printed.

Status

• [x] Code: Done
• [ ] Tests: TBD, help appreciated
• [ ] Wiki: TBD, help appreciated

For the wiki it would be nice to give some hints on what the Bootstrap 4 replacements for some of the things, see also https://github.com/twbs/bootlint/pull/410#issuecomment-327455304

/cc @XhmikosR @Johann-S

[Herst]

I've changed it now to more specific selectors where it makes sense. /cc @Johann-S @XhmikosR

[XhmikosR]

Isn't this ready to be merged?

[Herst]

Tests and wiki missing