Some tweaks to the recent files list

[zonkmachine]

.mpt files was already sorted out from the list but any other file is go. Instead we ban any file that isn't either .mmp or .mmpz from entering the list.
I also increase the number of remembered files to 50 ( Only 20 is shown in the menu and the rest is to fill out the space left from deleted files or removed external drives ).

Edit: Example of stuff let through to the list. The numbers are command line arguments leaked through.

  <recentfiles>
    <file path="../build/openlast.patch"/>
    <file path="3000"/>
    <file path="70"/>
    <file path="/home/zonkmachine/lmms/recover.mmp"/>
    <file path="300"/>
    <file path="30"/>
  </recentfiles>

[zonkmachine]

I'm cool with this solution. It works fine but I'm going to test it some more.

[Wallacoloo]

Previous logic treated the suffix as case-insensitive. It may be a good idea to change this to

if( recentFile.suffix().toLower() == "mmp" || recentFile.suffix().toLower() == "mmpz" )

In order to match this behavior.

[zonkmachine]

Thanks, fixed!

[zonkmachine]

Merging this. Thanks for the review!