Removed undo/redo event triggers for MAC also.

Removed CTRL+Z and CTRL+Y event. Now they will be handled by browser …

…default events.

[Yashpal] Added plugin for displaying and hiding preview.

Added Bower manifest file.

Merge pull request summernote#1164 from summernote/develop

v0.6.9

Merge pull request summernote#1163 from summernote/develop

v0.6.8

Merge pull request summernote#1086 from summernote/develop

v0.6.7

Merge pull request summernote#1039 from summernote/develop

v0.6.5

Merge pull request summernote#1015 from summernote/develop

v0.6.4