from Mckillo master: fixes, improved attachment tab, mailer, image deletion frontend

I tried to integrate McKillo's pull request into current master's code so it should be up-to-date now.
This replaces PR #675.

- changes on geostyle.css: Could someone check this?
- new script other.js: Seems to handle image removal (says add/remove attachments - ?)
- mailer plugin: added event/venue title to email subject - maybe we should make it configurable and/or limit character count?
- controller, image remove: Should become more save. In backend one can reuse an image so it shouldn't be removed in that case. I think we need to count the usage and only delete files if really unused.
- attachments tabs: I tried to integrate @JKoelman's changes

At the moment I have nothings tried out! Only merged dry.