Qtdesign

Changes:
QCard
- Removed methods to access trimmed list of internal QPushButton functionality
- Exposed internal QPushButton widget to allow more control over QCard behavior

QDesignLoader
- Significant rewrite to modernize and clean up internals

README.md:
- Now includes more information on the motivations behind QtDesign

Changes:
QCard
- Renamed QCardWidget to QCard
- Removed preset QGridLayout from widget to allow users to define their own
- Removed `addWidget()` method as it was tied to the preset layout
- Added QPushButton methods such as `isChecked()`, `setEnabled()`, etc.
- Added QPushButton signals `pressed` and `released`

QRichTabBar / QRichTabWidget
- Renamed `tabLabelText()` to `tabText()`
- Renamed `setTabLabelText()` to `setTabText()`

Bugfixes:
- QCard now works with widget promotion in Qt Designer
- QRichTabWidget `addTab()` and `insertTab()` methods now properly format html labels

New Features:

QtdWidgets:
- `QCardWidget` | Button that functions as a container widget
- `QRichTabBar` | Sub-component of QRichTabWidget
- `QRichTabWidget` | Allows the use of rich-text in tab labels

QtdTools:
- `QDesignLoader` | Implementation of uic equivalent for PySide2