Refactor CircleCI configuration (jjochen#250)

* use aliases to refactor executors in circleci config

* Refactor commands

* new line at end of file

* fix swiftlint command

* refactor circleci commands

* refactor executors in circleci config

* Reorder commands

* run tests on iOS 10 to 13

* use default xcode for tests on older iOS versions

* install missing simulator runtime on CircleCI (WIP)

* add missing "

* install simulator ftom circleci config

* fix start simulator command

* update dependencies

* update xcversion before installing simulator

* remove xcversion update

* fail to install simulator doesn't fail build

* allow higher nimble tolerance for two specific tests that failed on iOS 10

Co-authored-by: Jochen Pfeiffer <[email protected]>