renamed css class: filterableByTag -> stackr-filterable-by-tag
renamed css class: entry_tag -> stackr-tag
renamed css class: distinctEntriesTagList -> stackrs-tag-list
fixed: wrong id for context add div element
renamed ids for title and description fields of Context and Stackr div
renamed error classes to, e.g. credentials-error, and removed ids of span and replaced by classes
renamed css class: login-button -> button-login
renamed everything that has to do with registration -> renamed to sign up