Add setting to ask/not ask to open prev files on load

[mattpass]

At present ICEcoder asks if you want to open the previous files on load. It's likely you want to always open them rather than start with no tabs open, but it may not always be the case.

Add a setting to ask/not ask on load, and maybe look to have this set to not ask by default.

[mattpass]

Have decided to simply make opening the last files you had open the default and it doesn't ask.