Quill: Add possibility to clear copy&pasted content from HTML

[AntonLV]

• 1. Add possibility to clear copy&pasted content from HTML

• Froala does it by default.

• The problem is easily reproduced in FireFox.

Copy&paste in Chrome:

Copy&paste in FireFox:

Note. Currently available 'Quill - paste as plain text' setting doesn't help.

• 2. There is no a possibility to center a content that is embedded.

• 3. Heading styles in editor and on the view page appear differently, especially Headings 4/5/6

It appears because Quill adds their own styles which overwrite the same styles from Typography.

.ql-snow .ql-editor h4
.ql-snow .ql-editor h5
.ql-snow .ql-editor h6

[AntonLV]

@romanlesnikov
Re point №3: Some styles are still there.

Can we remove everything from 'editor_snow.quill.css' related to default HTML tags (H, P, LI, etc) styling?