I found .deb files in my cache for some webapps I installed. Then I used apt-get to install some other web apps. But the icons aren't showing up on the unity bar. How do I rectify this?
After you install a WebApp, it doesn't get added to your Unity Launcher like normal applications do. You actually have to visit the website in your browser and enabled/install it on that website. When you visit a website supported by or supports WebApps, you should get a little option bar or panel that asks you if you want to install or enable WebApps for that website. Once you click yes, you should see the icon appear in your Unity launcher and Dash. If you don't get an option bar/panel then most likely you have the website blacklisted.
Remove an “excluded” WebApp website in Firefox:
Note, by default, Firefox is the only browser that supports Unity WebApps; however, you can install an extension to allow Chromium to work as well. I believe the package name is: unity-chromium-extension.