[FEATURE] Add atlas preview toggle. Allows for navigating through atlas features and previewing the composition for each feature. Atlas maps can have their extent temporarily tweaked for each atlas feature.
[composer] Correctly shift overview frame when moving map item content
[composer] Make sure signals for overview extent changing are reconnected after loading composition
[composer] Recenter overview when checkbox enabled
[composer] Show status bar text with current atlas feature
[composer] Update features if atlas preview enabled and coverage filter/sort changes.
Protect against atlas with no matching features
[composer] Add atlas preview actions to new Atlas menu
[FEATURE] Add seperate controls for printing/exporting whole of atlas composition. Allows single features from an atlas to be printed/exported.
[composer] Update atlas filename expression when the expression actually changes
[composer] Also re-evaluate current features filename so that filename expressions take effect immediately
[composer] Make sure $feature has the same value in composer labels as it does when used in filename expressions
[composer] Make sure scalebars are updated during atlas previews
[composer] Add shortcut to atlas settings to atlas toolbar and menu. Designed to make atlas features more discoverable for beginners
[composer] Refresh main map canvas when atlas preview feature changes, allows for easier customisation of maps styled using $atlasfeatureid expressions