Content Packs small UI issues

While testing and looking at the new Content Packs functionality, I found some small UI or usability issues. @kmerz and I decided to compile them into a single Github issue, so they are grouped together and are easier to find.

Issues are described very briefly and some may also be personal preferences, so please let's discuss them if you disagree.

### Content Pack overview page
- [x] List is not sorted alphabetically
- [x] Installing a Content Pack does not update its "installed" flag on the list, a manual reload is required
- [ ] When a filter is applied, deleting a Content Pack will cause the filter to reset

### Content Pack details page
- [x] The Content Pack title is hard to find

### Forms
- [x] Enter does not submit most forms (e.g. parameter creation, installation)
- [x] There is no "cancel" button on create/edit forms
- [x] Save/Close buttons have different order than other pages in the product

### Others
- [x] When creating a Content Pack, we shouldn't allow using relative URLs (or at least not render them as links in the web interface)
- [ ] There are some alignment or positioning improvements:
- [x] Create parameter button could move to the right side and be aligned with the header title
- [x] Apply button could be aligned with other inputs
- [ ] Action cells should get enough space to avoid a breaking line between buttons
- [x] Elements feel very tight on the installation summary, but we have more room to use on the right side

## Your Environment
* Graylog Version: 3.0.0