Pull Request by @LuccaHellriegel

setup

npm setup with parcel as bundler and jest as testing framework: allows to include future packages, unit-testing and splitting the code into modules
added build and test commands to npm config

refactoring

split main code sections into modules
split up / extracted / renamed tons of functions for easier reusability / readbility / testability
made the most logic heavy functions mostly pure / removed direct roamsr-object access to allow trivial and mock-free testability / one-way dataflow
clarified dataflow in some functions to improve understandability
added status-tracking / minimal "state-machine" to allow a more "reactive" style in the future and make keybindings based on status possible
changed keybindings to a map-based approach to make future additions trivial
isolated all roamsr.state-mutations into functions for a better overview of what could change the state / prepare for reactive-refactor

a card is now only detected as new if it has no review-blocks, not if it has no refs on past daily pages
edge cases of limit-filtering when we mix multi-deck cards with single-deck cards generally work now (in some cases the limit of the higher deck still wins), added extensive unit-test for the filter-method
flagCard correctly steps to next card now
S-key keybinding fix (https://github.com/aidam38/roamsr/commit/e1acf6f7d6101a23ed75752b81ffaadf5b3ce67a)
extraCards are saved correctly (not as arrays) / will be accessed correctly
sessions only start if the refreshed queue is not empty, counters are updated if the queue is refreshed

"space" = "good" response (trivial via the changed keybinding approach and the status-tracking)
can configure if left sidebar should be close (https://github.com/aidam38/roamsr/issues/32), cant restore because of current Roam-state
mainTags is now an array / can use multiple main tags (https://github.com/aidam38/roamsr/issues/15) - breaking change for old settings!
the sorting-order of the presented cards can now be configured