when caret is at the end of blockquote and you press enter, create paragraph, not another blockquote

[linkesch]

Q	A
Bug fix?	yes
New feature?	no
BC breaks?	no
Deprecations?	no
New tests added?	yes
Fixed tickets	#294, #1054
License	MIT

Description

We had this reported a bunch of times. When you place a caret at the end of a blockquote and press enter, a new blockquote is created instead of a plain paragraph and you have to press backspace to get rid of it. This is not a standard behavior. When you do the same with other block elements (h1, h2...) you will get a paragraph as expected. For some reason, this doesn't work with blockquotes.

Also when you try it in other "standard" editors (Word, Pages, Google Docs...), it behaves as expected - on enter you will get rid of the current "style" and start a new plain paragraph.

This PR solves this problem and forces a new paragraph after pressing enter at the end of a blockquote. Pressing enter anywhere else in the blockquote is not affected.

[coveralls]

Coverage increased (+0.01%) to 94.986% when pulling e497496 on create-paragraph-on-enter-in-blockquote into 77e941a on master.