started replacing store with DAV-Dump

DAV-Dump is based on Taskard's original implementation

note that I have yet to figure out how to get response headers from
`jQuery.ajax` (without resorting to `getAllResponseHeaders`)
refactored store handling

note that tasks' associated projects are currently being discarded (cf.
inline comments)

not entirely sure it still makes sense to use a separate `Store`
instance for each project: the original idea was to keep the store
implementation as simple as possible and for projects to be independent
from each other - but it seems like this leads to overwhelming
complexity here for orchestration purposes

yet, while it should be easy to adjust DAV-Dump's create/update/delete
functionality to support subdirectories, an index supporting nested
entities would be far less simple
fixed project names