Refactor devsel to allow for multi-device filters

No multi-device filter yet implemented or tested
Dev. sel.: rename single/multi filters to indep./dep. filters
Add indep. and dep. platform filter, not tested

Indep. filter: devices must belong to a platform specified in the
filter data parameter.
Dep. filter: devices must all belong to the same platform (namely
the platform to which the first device belongs to).