Allow multiple <Kanban> elements on the same page

[dev-guy]

Currently only one component can be created by an application because store objects (e.g., $columns) are module-scoped variables (singletons).

First, each <Kanban> component needs it own store. This can be fixed with Svelte contexts. Another benefit of this change is that the memory related to a board will be released when it is no longer visible. This will be done in #60.

Secondly, when one page contains two boards arranged vertically, dragging a card in the lower Kanban board causes a card in the upper board to move. Example: https://github.com/V-Py/svelte-kanban/assets/12297328/0d0e751b-4f34-4a65-83b8-36499aeef950

Changes Needed (beyond #60)

1. Replace getElementsByClassName with getElementById using Cards' new id properties as described in Assign unique ids to boards, columns, and cards #61
2. Change the value of id attributes from card-A-col-B to board-A-card-B-col-C using the board's id as described in Assign unique ids to boards, columns, and cards #61
3. Call getElementId using the new value describe in 2 above
4. Column.svelte creates elements with ids like title-column{index_col} .. this is a good time to fix the spelling error for input-colum{index_col} (the n is missing). The board id should be added to these ids.
5. Scan the code for other instances of id="