Pyipam

Updates
* Updated navigation to show "about" page.
* Updated "add_subnet" function to spawn a process thread upon creation.
* Updated "add_subnet" function to verify a subnet doesn't already exist before adding.
* Refactored server.py startup script to make app more efficient and reliable.
* Refactored db class to reconnect to the DB on connection drops.
* Switched to use "waitress" as the WSGI server.
* Tidied model structure.

Fixes
* Fixed subnet threads bug that occurred when deleting a subnet.

Updates
* Updated IP address view so as to limit it to 100 IP's per page (added page navigation).
* Improved performance of application.

Fixes
* Fixed pings from Alpine Linux.

Updates
- Improved code notes.
- Minor tidy of controller code.

Fixes
- Resolved some ping inconsistencies when running from a Linux host.
- Resolved app setup issues / fully enabled the functionality.

New Features:
- Ability to add and manage subnets
- Scanning of IP addresses within an added to subnet to check availability
- Reverse DNS checks of IP addresses within a subnet
- Easy in-line editing of IP assigned hosts / notes
- IP search functionality