Added a missing 1.43 readme credit.
Changed startup to attach exception handlers slightly differently. WinForms Application exception handler is only attached when WinForms is run, preventing these assemblies being loaded on Mac (harmless but not ideal behavior since they are not used and just delay startup).

Changed MainForm load timer to be more sensible when reloading.
Minor cleanup and tweaks:

- Used "start" as the common term for starting the program in the readme.
- Used ReadOnlyDictionary in IniLineParser to protect some of the fixed dictionaries.
- Removed generic term for PonyBase in TryParse delegate.
- Reused list of interactions as synchronization object in PonyCollection.
- Added missing implementation for TryGetValue in ReadOnlyDictionary.
- Tweaked ImageSize parsing of GIFs to throw with standard error message.
Refactored screensaver startup into a separate method in PonyStartup.
Added list of required packages required under Linux for Desktop Ponies to run (might be worth looking into creating a package for Ubuntu/Debian sometime...). Sadly there doesn't exist a ".NET Framework 4.0" package that mirrors everything that Windows would install, on that other hand that would be silly given package management exists...
Added a top-level readme about the project.