* Split install steps into git clone and composer install
This gives the admin a little more knowledge about how to maintain the system, showing them composer_wrapper.php and su - librenms
They will get errors if composer_wrapper doesn't work because of a proxy or no internet connection
We lose stats on packagist.org (https://packagist.org/packages/librenms/librenms/stats)
If we wanted to keep stats, we could use:
```
COMPOSER_ALLOW_SUPERUSER=1 composer create-project --no-dev --no-install --keep-vcs librenms/librenms librenms dev-master
```
not sure that is worth it.
* fix composer_wrapper.php path
* Add 18.04 install guide and and move 16.04 guide
Adds 18.04 install guides to "Installing LibreNMS" page.
Moves 16.04 install guides to "Old install docs" section.
* Update index.md
Update index tree to 1804 over 1604
* docs: Continue to reorganize things
Make landing pages for /Installation, /API, etc.
Split API out into multiple docs
Properly use multi-level navigation
Add lower nav buttons (tops are bug so disable for now)
Add logo for fanciness
Refine index page a bit
* Improve API TOC layout
* Couple of fixes.
* Fix API/API-Docs, assumed it was at the right url.
