Fix hidden placeholder content override

When a user sets a data placeholder, they really want a placeholder.

Set content to !important and ensure it's not overridden (e.g. by Bootstrap).

Closes #255

Signed-off-by: Nick Semenkovich <semenko@alum.mit.edu>
Merge pull request #256 from semenko/master

Fix hidden placeholder content override
Upgrades dev dependencies
Update README.md
Disables, for now, important rule at csslint because of placeholder content fix
Merge pull request #238 from yacomink/master

disable toolbar within inserts
1.9.0
Add support for tab based indenting and outdenting of UL and OL
add anchor target option
target blank option working, looks horrid
Add a save button to the anchor form, add classes to the form as not to rely on non specific selectors
remove overqualified selectors
prevent default link action on the save link
Merge pull request #279 from createdotnet/tab-lists

Tab based indenting and outdenting for list structures
Merge branch 'link-target-option' of github.com:createdotnet/medium-editor into createdotnet-link-target-option

Conflicts:
	dist/js/medium-editor.min.js
Merge branch 'createdotnet-link-target-option'
Formatting