Annotation functionality for graphs can be ported from dashiki

As discussed in the tasking meeting, one idea could be having a set of pages on-wiki under a json namespace that store the annotations.
Those would be divided in 3 levels:

Level 1 (one page):                                                re. all metrics

Level 2 (3 pages):           re. contributing metrics            re. reading metrics              re. content metrics

Level 3 (N pages):  re. metric 1       re. metric 2       re. metric 3      ....................................                re. metric N

• The annotations stored in the "all metrics" file of level 1, would be shown for all metrics.
• The annotations in a level-2 page, would be shown only for the metrics corresponding to that category: contributing, reading, content.
• The annotations in a level-3 page, would only be shown for the metric in question.

The level-3 pages could be named after the corresponding metric (using a given convention), so that Wikistats knows how to access them, without keeping config?

Question remains, whether the annotation pages themselves should keep track of the 3 level structure by i.e. a link to the parent (and let mediawiki-storage handle indirections), or have Wikistats itself know the 3 level structure and request for each metric: the metric annotation page, the category annotation page, and the top "all metrics" page and merge them together.

As discussed in tasking, I'm breaking down this task into:

• model an annotations schema that makes it easy for the UI to render
• find or implement a way to visualize annotations in d3 line, bar, table, and map charts
• program an API that reads current Dashiki-style annotations from meta.wikimedia.org and transforms them to the wikistats format. Keep it generic so we can switch out the storage later
• link back to the annotation wiki pages from the metrics that render them
• organize meta pages and documentation so that community members can intuitively understand what they're used for (add some descriptive metadata to the schema)
• (low) improve the Dashiki mediawiki extension to render annotations in a friendlier layout
• (lowest) add a way to select a time period on wikistats and add an annotation
• (lowest) add a way to pop up a form on meta to add an annotation by editing the underlying json

@Milimetric: i have transfer most dashiki annotations (there were not that many) by hand, is this task still needed?