Fixed an issue with removing first menu item in RemoveMenuItem (#166).
Added package `FindTopMenu` method (#166).
Removed menu separator from the Tools menu.
Improved `ffitoapi` tool logic when no replacement is made.
Refactored `tools` interface to make it easy to add/remove tools.

The tool command (`exec.fn` method) now accepts `filename` as the first
parameter instead of `wx.wxFileName`.
Added package `AddTool` and `RemoveTool` methods (#166).
Added handling of `~` in launch command path.
Updated package `GetRootPath` to accept file/directory name (#166).
Added package `GetKnownExtensions` method (#166).