Issue #39: Landing page content (membership splash, events list blocks)

[lilliputten]

• Added membership splash for logged (only text) and non-logged (text and visual) users. (The action button is temporarily linked to the main page.)
• Adaptive layout: trim too long title string with an ellipsis.
• Removed unused 'onevent' templates.
• Added can_register method to the Event data model, the 2nd events list on the main page: to show user's own event (where they already made a registration), data preparation for this second list. Utilized original events-list-block.django asset to display any kind of events list.
• Updated version: 0.0.14.

Splash view for the logged user (text only):

Splash view for non-logged user (text and visual):

Adaptive layout (trim title on small screens):

[lilliputten]

Rebased conflicting main branch. Updated definition and usage of event.can_register.