Spinner, Range Inputs and various fixes

• fix: Dropdown only shown dropped once. Surfaced first in later version of chrome.
• added: Spinner module for easily creating (css only) spinners. Example (Note: Need to use at least Bootstrap 4.2/4.3 css)
• added: Range input/slider. Tx to @Munksgaard for contributions. A simple example here
• added: Support for custom labels in Radio and Checkbox
• added: Scrollable body and custom attributes to Modal
• fix: Expose centered option for Modal
• added: Add support for plaintext input
• added: submitButton and resetButton shorthand functions to Button module
• update: CDN module now points to Bootstrap 4.3.1 css.
• minor: Some doc fixes. tx to contributors for issues and PRs here!