Add id value on start

It useful to have one id for every math element and now it is
setup in the start.
Changes in Makefile
Add demo for Firefox OS

This is a modify version of the proof of concept for Firefox OS.

TODO:

* Add note in the documentation.
* Improve building.
* Fix bug when get element to process.
Some improves in the Firefox OS demo

* Improve the layout of the demo (adding gaia's headers).
* Some how the selection bug was fixed.
Add minimal examples to Firefox OS demo
Create a function to delete equations

The few lines that add a buttom to delete equations have been move
to a function and add a parameter that switch the buttom to be
visible or not (the case for the original equation).
Improve in Firefox OS demo

* Improve compatibility with Firefox OS Guidelines.
* Some changes in documentation.
Using mathmlCreateNode function

Replace some duplicated code with call to mathmlCreateNode.
Replace mathcolor with background-color

With background-color is easy to say of with element the mouse
is over.

The choice for orange as the background-color was because of a good
contrast with the white background and the back font.

Note: Look like that margin and padding doesn't effect mathml
elements. And border don't have a uniform behaviour.
Initial support for drag and drop

* Add first support for drag and drop (across equations).
* Change mathmlSetup to cover drag and drop.
* Add simple example of drag and drop.
All events start with a single click

* Refactor the code so that all events start with a single click.
* Remove some jQuery call when not need.
* Remove partially duplicated function to replace mi element with mn.
Some changes in CSS of Firefox OS demo
Compact Firefox OS demo into one file

The Firefox OS demo is store into only one HTML file now and use
some Javascript lines to change the content.
Fix align of undo button

When the equation's height is small than button's height the buttons
will not be aligned. We change the CSS to fix this but now one
button can cover part of another.
Update demos

For Firefox OS some changes was made and now the demos was updated.
Update documentation

* Remove information about double click in documentation.
* Remove information about double click in source comments.