NEXXT 2.1 - addressing some issues and wishes

This update combines some hotfixes with minor user requests. 

Prefer your own custom subpalettes loaded when the program starts? This version can do that. 
In full; here's the changelog. 

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2.1.0
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New features:
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Startup, subpalette user defaults:

• When NEXXT starts, it will look for a 64 byte long file in its home folder
  called "default_subpals.pal". If present, the contents of this file will
  overload the built in default. 

• In addition, it will look for 4x 16 byte files named "default_subpal0.pal"
  and so on. If present, these will overload individual subpalette sets. 

There are three new menu items to help set up user defaults. Find them under {Menu > Startup defaults}.
They are:

• Store all 4 sets as new default: 
  Takes the contents of all 4 subpalette sets and creates a new startup default.
• Store this set as new default:
  Takes the contents of the current subpalette set and creates an overloading startup default. 
• Reload defaults: Just like the startup process; it first sets all sets to the internal default, 
  then looks for a 64 byte default to overload it with, then patches any 16 byte defaults on top.

Minor changes:
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Loading session:

• Main Editor changes caption to "loading..." while in the process. 

Patterns menu:

• Arrange submenu renamed to Sort & Arrange, 
  to improve discoverability without making the parent menu any longer.

Bugfixes:
---------

Tiles tab [F3]:

• -Fixed the following canvases updating at wrong scale while on the Tiles tab:
  chr bank swapper, chr bank selector, metatile, metatile editor.

Type In mode:

• Fixed keys [! " # $] (US english keyboards) not registering.
• Fixed keys [  @ £ $] (some intl. keyboards) or any other symbols 
  that may be on alt + 1...4 not registering.
• ASCII offset control behaves consistently when dragged, and may be dragged both up and down.

Chr Bank Swapper:

• Fixed a situation where the selection box could be expanded out of bounds.

Chr Bank Selector:

• Fixed a situation where the selection box in 'free mode' could be expanded out of bounds.