timeline layout fix liquid sort issues

[evanwill]

Liquid doesn't sort numeric stuff correctly.
Add the sorting to cb_helpers plugin as a ruby function instead, like array_count_uniq, could be specific to the timeline-style layout or just sort of implement the numeric_sort that could be used anywhere.
Consider case of BC dates (negative years) and years < 1000 CE.

• sort_numeric plugin
• consider handling of non-number values and nils
• rewrite timeline date parsing to avoid nils and support negative years
• consider combining with array_count_uniq or cb_helpers or keeping all separate

[evanwill]

working in branch "update-plugins".