Add command line debug mode support for browser

Browser can be launched with -debugMode argument. When launching
in debug mode an overlay is drawn on top web content.

Currently debug mode only contains content height, content width,
scale, and a button for dumping memory snapshot.

For dumping memory info from command line following can be used:
```
sailfish-browser -dumpMemory [fileName]
```
Browser also exposes dumpMemoryInfo dbus method taking a file name argument. Memory dump works only within debug mode. In normal mode, dumpMemoryInfo doesn't do anything.

Requires: https://github.com/tmeshkova/embedlite-components/pull/56