Drop support to BBB 0.7 and add basic support to 0.81

Very basic support to 0.81 for now. Still have to include all new methods and
parameters.

refs #1129
Remove parameter 'random' from getMeetings

Since BBB 0.8 this call doesn't need parameters anymore.

refs #1129
Review all methods responses and documentation

The only change in the code is in the response of getMeetings, that now returns
more attributes that have to be properly parsed by this lib.

The new parameters for the API calls 'join' and 'create' that were added in
BBB 0.81 are already supported.

refs #1129
Allow all methods to receive custom parameters

Useful for development or for custom versions of the API. With this, all the
methods that generate URLs accept an optional hash with parameters that will
be added to the URL as they are passed, without restriction or validation.

refs #476
Remove join_meeting, should always use join_meeting_url

join_meeting was a method that actually sent the join request to the server.
But there's no real use for this method. In practice, the application gets the
join url (via join_meeting_url) and redirects the user to this url.

refs #1129
Add .bundle/ to .gitignore
Add first version of getDefaultConfigXML

Tests not updated yet.

refs #1129
Add a first version of setConfigXML

Without tests for now, but with an example file.

Also includes ordering the parameters in the URL. If not order, it will fail
when calling setConfigXML. More discussion about it at:
https://groups.google.com/d/msg/bigbluebutton-dev/A9-QaNLhbZ4/MKMGv7ztHLsJ

refs #1129
Add helper class BigBlueButtonConfigXml

To help users to modify config.xml files.
First version, still needs more documentation and tests.

refs #1129
Generate cleaner config.xml that can be passed to setConfigXML

If the config.xml passed to setConfigXML has line breaks, it won't work.
So now we generate a cleaner XML without line breaks or indentation in the
class BigBlueButtonConfigXml.

refs #1129
Fix API calls that pass params with keys both as strings and symbols

Parameters can be passed with keys as symbols or strings, but sorting these
keys was generating errors if the types were mixed.
Fixes the error 'comparison of Array with Array failed'.

refs #1129
Add class and methods to get the list of layouts

To make if easy to get the list of layouts available in the server. Can also
be used in the future to redefine layouts.

refs #1129
Improvements in BigBlueButtonConfigXml

Don't break if initialized with an empty XML and added #is_modified?

refs #1129
Fix the way we check if a config.xml was modified

Wasn't copying the xml properly, and the comparison to see if it was modified
was always returning false. Using a deep copy now that fixes it.

refs #1129