Changes per Issue #4 - Battery State Display could be customized with parameters

[slgrobotics]

See Issue #4

Working code at https://github.com/slgrobotics/articubot_one (use "dev" branch)

Here is how parameters look in a launch file:

https://github.com/slgrobotics/articubot_one/blob/dev/launch/launch_rviz.launch.py

rviz_overlay = Node(
    package='battery_state_rviz_overlay',
    executable='battery_state_rviz_overlay',
    namespace=namespace,
    parameters=[{
        'use_sim_time': use_sim_time,
        # see https://github.com/slgrobotics/ros_battery_monitoring/blob/main/battery_state_rviz_overlay/src/battery_state_rviz_overlay_parameters.yaml
        'width' : 450,
        'height' : 10,
        'line_height' : 25,
        'horizontal_distance' : 20,
        'vertical_distance' : 20,
        'font' : 'DejaVu Sans Mono',
        'text_size' : 15.0,
        'horizontal_alignment' : 0,
        'vertical_alignment' : 3,
        'bg_color_a' : 0.1,
        'fg_color_rgba' : '0.0 0.8 0.6 1.0'
    }],
    output='screen',
    remappings=[('battery_state','battery/battery_state')]
)