Add the popular impressConsole.js from Lennart Regebro.

Press 'P' to show a speaker console in a separate window.

Supports:
- Navigation controls
- This slide and next slide preview screens
- Speaker notes
- Clock and timer

Also applies this patch, which makes impressConsole.js follow the new
impress.js plugin standard: regebro/impress-console#22

Note: As impressConsole is now a plugin, it is included by default. You
no longer need to include it with a separate <script> tag. Nor do you
need to call its init() method.

src/plugins/impressConsole/README.md

@@ -0,0 +1,33 @@
+Impress Console Plugin
+======================
+
+Press 'P' to show a speaker console window.
+
+* View of current slide
+* Preview of next slide
+* Speaker notes (contents of a <div class="notes"> element on current slide)
+* Navigation
+
+For speaker notes, add the following anywhere inside a step
+
+    <div class="notes">Speaker notes text...</div>
+
+Example CSS:
+
+    /* Hide notes from the actual presentation. This will not affect the visibility of notes in the impress console window. */
+
+    .notes {
+        display: none;
+    }
+
+
+
+Credits
+-------
+
+* Henrik Ingo, henrik.ingo@avoinelama.fi, impress.js (plugin) integration
+* Heiko Richler, Aico.Richler@gmx.net, major changes in rev. 1.3
+* Lennart Regebro, regebro@gmail.com, main author of impressConsole
+* David Souther, davidsouther@gmail.com, author of the original notes.js
+
+MIT License