[New Feature] Add Schema Diagram Panel

Details for the issue

An informative feature I miss from other commercial browsers is a graphical representation of the underlying db schema. While they often support input mechanisms to create tables and fields, I would be happy with just a movable/resizable static representation of the current db. This would allow printing and sharing concepts in the db design and evolution with end users.

Useful extra information

I'm sure the DB4S developers would have a blast coding up the graphical view of the loaded db. :)
And it could expand over time to include input mechanisms that update/modify the db.
QT Modeling

I'm opening this issue because:

• DB4S is crashing
• DB4S has a bug
• DB4S needs a feature
• DB4S has another problem

I'm using DB4S on:

• Windows: ( 10 Pro__ )
• Linux: ( distro: ___ )
• Mac OS: ( version: ___ )
• Other: ___

I'm using DB4S version:

• 3.10.1
• 3.10.0
• 3.9.1
• Other: ___3.10.99 build 171205

I have also:

• Tried out the latest nightly version: https://github.com/sqlitebrowser/sqlitebrowser#nightly-builds
• Searched for an existing similar issue: https://github.com/sqlitebrowser/sqlitebrowser/issues?utf8=%E2%9C%93&q=is%3Aissue%20

The issue names no source files, tests, or entry points to begin with. Start by locating DB4S's existing database-schema and desktop UI code, then review the linked Qt Modeling example for the intended presentation. Done would require a movable, resizable static diagram of the loaded SQLite database that can be printed and shared.