Use last opened file for open file dialog

[kettek]

As it says. When a file is opened, its location should be recorded and used for future file open dialogs. Alternatively, file open dialogs could use the location of the currently opened file.

[kettek]

Default path for file open dialogs seem to differ according to operating system.

Windows recalls last opened position. Linux seems to use a base default location of "Recent" or whatever it is. Mac OS needs double-checking.