SeriesServiceImpl: extract Price.valueOf() method.

No functional changes.
SeriesServiceImpl: simplify code.

No functional changes.
IDEAS.txt: added
-1: updated series/info prototype.
-1: added prototype for collection/info
ADD_SERIES_TO_COLLECTION -> UPDATE_COLLECTION
-1: implemented basic controllers.
+2 ideas
added servies with fake implementation
updated IDEAS
Added entities.
-1: create collections for existing users
finally implemented methods for add/remove/contains series in collection
-1: implemented collection info page
-1: show flash messages
updated NEWS
updated migration
+1 tech debt records and fixed typo
added togglz+thymeleaf integration
updated IDEAS