Make background page objects aware of page variables

[vollstock]

This example shows a techical drawing with a data field.
This is my literal use case. It utilizes the global standard placeholders (e. g. %pagenumber%).

However, I often find usecases where I want to add additional fields on a per page basis like e. g. a document status (draft, final, etc.) or author. This is similar to feature request #480 which asks for document-wide placeholders which could be useful, too but are not a necessity for background pages as in this case static text works just fine.

The example given in #480 could work wonderfully, if only background page objects could use page variables.

Example

• A text field on a background page uses variable %author%.
• On the background page the variable is set to Alice.
• Each page will now show the name Alice.
• Some pages however may define a different author. Still using the background page object but overwriting the placeholder value.

[stale]

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[davidjgraph]

Locking issue due to +1 spam. https://hackernoon.com/45-github-issues-dos-and-donts-dfec9ab4b612