Update "components" documentation page

[debbabi]

Update this documentation page http://cohorte.github.io/docs/1.1/components/ to talk about :

• how to prevent exporting (a part of) service as remote service
• explain the logic of consuming a service (among local / remote)
• service priorities
• how to bind to a list of components providing the same service (aggregation)
• using standard services (http, ..)

[ogattaz]

Add samples :
a) in the § "3.3 .Net support"
ours Unity samples
a sample where a C# class is extended by an IronPython class to become a Pelix component
b) in the § "3.4 Other legacy code"
our lib C wrapping sample

[debbabi]

Add documentation about how to target specific group when exporting services.
See #68