agl-demo-control-panel: Refactor Settings, Config and UI scaling

agl-demo-control-panel: Refactor Settings, Config and UI scaling

V1:
    - Add template to specify new configs in config.ini
    - Add drop-down to load all configurations specified in config.ini
    - Add new assets and refine UI elements (Scaling issue fixed)
    - Add size grip to main window
    - Add options in settings to configure port and AGL's CA.pem file
    - Removed unused or redundant files

V2:
    - Check for user configs agl-demo-control-panel.ini & config.ini
      before resorting to default config.ini
    - Check for CA.pem and jwt tokens in default paths
    - Add new fields in settings for CA.pem file, jwt token path, TLS Server name
    - Fix crash in dashboard.py module due to icon.availableSizes()

V3: Add Start/Stop states for the client

V4: Block subscription event updates to the UI when values are changed on the control panel

Bug-AGL: SPEC-4905

Signed-off-by: suchinton2001 <suchinton.2001@gmail.com>
Change-Id: Id7883ba3bc88248dabb58d54e6e931f6d365fd54