UI Adjustments

[zafodB]

Further adjustments to UI, particulalry in relation to theming. Important changes:

• Wider adoption of dark mode - Dark mode has been adopted in several new fragments and UI elements, such as attack record details, filters, statistics
• Accessibility adjustments in light mode and dark mode - both light and dark theme were adjusted to avoid unreadable text in UI (light colour text on light background/dark colour text on dark background)
• Simplified and streamlined colour adjustment - app theming has been adjusted to allow simpler modification of color theme. In this version, theme can be adjusted by changing colorPrimary and colorPrimaryVariant in colors.xml, separately for light mode and dark mode.
• Action buttons moved to Action Bar - action buttons, such as filter, group, or delete were moved from a custom bar on the bottom of the screen to a more usual location in the Action bar (top right of the screen). This affects RecordOverviewFragment, RecordDetailFragment and StatisticsFragment.
• Date and time selection adjusted - date and time selection fragment, displayed when applying filters in the Records or Statistics screen has been replaced by a flow: a date picker is displayed, and only after the user has selected a date, a time picker is displayed. After the user has selected time, the value is passed to the filter.

Fixes #178

[sastry17]

changes tested and approved.