Fixes to scope

as discssued in
https://github.com/twbs/bootstrap/issues/15117#issuecomment-63029993

- added ``scope="row"`` to row headers
- made sure row headers are actual ``<th>`` elements
- removed ``scope="col"`` where it was redundant
- simplified table examples with (to me) unnecessary
``rowspan``/``colspan`` (unless you really want complex tables, in which
case we would need full-on ``id`` and ``headers`` attributes to make
sure each table cell has an explicit association with the related header
cells - overkill, in my opinion)
- one table (in typography) left header-less, as it's more or less presentational (though its structure is still important, hence not adding ``role="presentation"``)
Add a target to generate the gh-pages files.

It sets `github: true` for us.
Fixes #15074: Fix the nesting problem with form control size variants
grunt
Alternate fix for #15250 with a more descriptive theme jumbotron
Fixes #15140: Restore more missing .media styles from shipping #14801
grunt
Fixes #15241: Add simple example to docs for collapse plugin
Merge pull request #15133 from patrickhlauke/docs-table-fixes

Fixes to scope
Fixes #15096: Fix navbar forms in the non-responsive example
Bump Glyphicons to v1.9
Merge branch 'master' of github.com:twbs/bootstrap
Merge pull request #15134 from twbs/docs-gh

Add a target to generate the gh-pages files.
Update devDependencies.
Merge pull request #15183 from twbs/deps

Update devDependencies
Example: minor image compression improvements.

[ci skip]