Brief 2.6.0 alpha 1

This is an alpha release of the 2.6 series featuring the new Brief feed preview interface and fixing the "unable to subscribe" problems in Firefox 64+, and also including a lot of internal improvements including eslint integration and basic config, migration to ES6 modules, better default / user-set preferences differentiation, cyclic dependency removal (not complete yet) and many other minor changes.

Note that this is an alpha version, and you should be ready that it can contain weird bugs and misbehave in interesting ways.

Changes since alpha 0:

• fixed a bug with restoration of discarded tabs (feed preview detector false positive)