feat(feature-detect): detect if backdrop-filter is supported

Currently `backdrop-filter` is only supported by Safari and it allows web developers to implement awesome background blur effects like a native iOS app

chore(ionic): release beta.8

Merge pull request ionic-team#6761 from Merott/hardware-typo

docs(platform): correct a minor typo of "hardware"

chore(ionic): release beta.7

release: v1.3.1 "el salvador"

style(toast): fix linter error

chore(packaging): dependency version updates

Removed redundant this.nav declaration (ionic-team#6244)

`this.nav = nav` is already present due to the `public nav: NavController` declaration, having it in the constructor as well is redundant

chore(sass): fix Sass linter errors

chore(package): update README