- allow passing of custom param (logo) to override default logo

.../main/java/org/bigbluebutton/api/ParamsProcessorUtil.java

...b/src/main/java/org/bigbluebutton/api/domain/Meeting.java

...button-client/src/org/bigbluebutton/core/model/Meeting.as

...rc/org/bigbluebutton/main/model/users/EnterApiResponse.as

...ent/src/org/bigbluebutton/main/model/users/JoinService.as

...ent/src/org/bigbluebutton/main/model/users/UserService.as

...-client/src/org/bigbluebutton/main/views/MainToolbar.mxml

...rs/org/bigbluebutton/web/controllers/ApiController.groovy