Functions to hide for later consideration

[antagomir]

Move the following functions to /inst/extras/ to be discussed later, and either remove them from examples or show some of them with standard ggplot:

• analyze_metadata (need to discuss design choices on data structures)
• all visualization functions depending on analyze_metadata

(Later: Consider overlap in functionality with the fennica R package (this is also metadata) in terms of analysis and visualization functionality and consider possibility for a separate package for generic metadata analysis/visualization that could be used by both finna and fennica when they share the data structure.)

[antagomir]

Finna package scope is mainly in information retrieval and less on downstream analysis (as many of those tasks already have standardized solutions in other packages).