The following getters have been only used in the context
of initializing fetched raw data using the functions from
roadmap_item_utils.js:

getters.lastTimeframeIndex
getters.timeframeStartDate
getters.timeframeEndDate

Having these coupled to vuex makes it hard to generate-
mock data needed for testing, thus we are moving them
into roadmap_item_utils.js to use as pure helper functions.