[keycloak-dev] Update to 3.4 release dates

[Stian Thorgersen]

Update release dates:

* 16 October - Feature freeze! Only bug fixes after this point please
* 30 October - 3.4.0.CR1
* 6 November - 3.4.0.Final
* 20 November - 3.4.1.Final
* Mid December - master switches to 4.x

Community contribution deadlines for 3.x:

* 12 October - deadline for feature requests and bigger enhancements
* 26 October - deadline for small enhancements
* 1 November - deadline for bug fixes

Anything contributed after these dates will most likely not be 
reviewed/merged until 4.x