Create a custom LFE Bootstrap theme

[oubiwann]

We're using Bootstrap; let's make it our own. See also ticket #65.

(This has already been done -- creating the ticket to record the task.)

Part of epic #66

[oubiwann]

Most of the work was done here:

• Update CSS lfe-deprecated/docs3#7

[oubiwann]

The current development theme is available here:

• http://docs3.lfe.io/dev/design/bootstrap.html

Note that once we merge docs3 into docs, that will be here:

• http://docs.lfe.io/dev/design/bootstrap.html