Pocketbase: Load older journals

[lukas-h]

• [ ] Implement logic to PagesStore to add new journal in the past, if it doesn't exist yet. (right now we only statically create 30 entries in the beginning and don't allow to navigate back further in time. This should be possible now though)
• [ ] Implement pagination based on pocketbase (1 request "getList" should fetch 30 the previous journals)
• [ ] If there is no entry for a previous item in the database, it should be created.
• [ ] Auto fetching of older journals based on switching to the previous journals via button (if 3 away from the last journal that is loaded, fire a request to pocketbase)

[lukas-h]

@shreyjotangiya This will be your first task. Right now, the logic is, that there are only the last 30 journals loaded. After that, the navigation just stops.