DEV-682 - grab bag of small tweaks

[respinos]

All about login:

• have the login modal default to using the sdrinst from HT.prefs
• if filterText is passed to FilterableSelection, check that item and filter the list
• add a "clear filter" button to the filter input

All about accordions:

• remove the active background color from accordion-header
• tweak the padding so header and body elements align
• remove accordion-body padding if it contains a list-group (see example)

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[carylwyatt]

merge away! ✨