[PLAT-6458] Add an AnalyticsEnvironment to allow customisations

Will allow an OG instance to have analytics parameters
e.g. model daycount to be set before entering analytics
[PLAT-6548] Remove ThreadLocalAnalyticsEnvironment
[PLAT-6548] rename AnalyticsEnvironment.init()
[PLAT-6548] Make AnalyticsEnvironment.setInstace() static

Reorder class layout & fix javadoc error
Merge pull request #46 from OpenGamma/topic/AnalyticsEnvironment

AnalyticsEnvironment added

PLAT-6548 #resolve Merged analytics environment