Allow to create custom pages and add them to the menu.

[silenceway]

This PR creates a new link in the admin page to go to a list of pages or allows to creation of new pages.

It saves basic page information in the database and it creates a markdown file in a pages directory within the config folder.

It shows pages in the sidebar before the books list or after the About link.

Pages can be enabled or disabled to hide them.

[digitalfredy]

@janeczku

Thanks for this great Open Source Project!

Will be appreciated if you take a look to this PR because we need to add some legal stuff like the Privacy Notice in our public library and will be great if we can have it from mainstream (we want to avoid hacks to get it done)

[digitalfredy]

@OzzieIsaacs I notice you merged some stuff recently, could you take a look to this MR?

[alejandrok5]

you could also do

Suggested change

	page = ub.session.query(ub.Page).filter(ub.Page.id == file).first()
	if page:
	try:
	page = ub.session.query(ub.Page).get_or_404(file)

And then check my comment after line 51
https://flask-sqlalchemy.palletsprojects.com/en/2.x/api/#flask_sqlalchemy.BaseQuery.get_or_404

[silenceway]

It shows an error with get_or_404, added try.

[digitalfredy]

@silenceway

In case your code enhances features of Calibre-Web: Create your pull request for the development branch if your enhancement consists of more than some lines of code in a local section of Calibre-Webs code. This makes it easier to test it and check all implication before it's made public.

From: https://github.com/janeczku/calibre-web/blob/master/CONTRIBUTING.md#contributing-code-to-calibre-web

[alejandrok5]

LGTM 🚀 !

[apollo1220]

@OzzieIsaacs could this be considered to be pulled in? This would be a really useful feature.

[OzzieIsaacs]

@apollo1220 You could speed up the process by writing some tests (https://github.com/OzzieIsaacs/calibre-web-test).