Django-bootstrap-swt

Bug fix
* loading spinner and error div selecting was broken

New components:
* [Alerts](https://getbootstrap.com/docs/4.0/components/alerts/)

API changes
In this release the api of the Modal component becomes changed:
* param: `title` renamed to `header`
* The [Modal](https://getbootstrap.com/docs/4.0/components/modal/) component contains now `ModalHeader`, `ModalBody` and `ModalFooter` or even strings instead of using the predefined class based components like discussed in #29.

First major release
This release contains the following features:
* Supports the following Bootstrap components:
* Tooltip
* Progressbar
* Badge
* Links
* Button
* Modal
* Card
* Accordion
* Buttongroup
* Dropdown
* Listgroup

* Async content fetching with ajax for Modal and Accordion component

* refactors all small BootstrapComponents to use the new Tag class for template rendering
* adds the feature to update the html attributes before rendering
* renames some function attributes to become clean naming

* fixes setup.py - no subfolders with static files were included in our builds

Refactors the following:
* Div component becomes a generic Tag component
* Removes the unused request argument from RequestHelper constructor
* adds the functionality to update the querystring of BootstrapComponents with url attribute