Rename line checkboxes in Grammar Settings

[jkornelsen]

Morpheme Line 1
Morpheme Line 2

Line 1 will be checked by default.
This will break compatibility with settings,
requiring the user to change checkboxes.
The most common use is to just use one line,
so we want that transition to be smooth.
So have new user var names,
and ignore the old ones.
So it will default to Line 1 checked.

Make sure it doesn't matter to LingTools if for example the Tamil script is
in Line 2.

Toolbox orthographic tags will be line 1?
But then the default of using line 1 will use only orthographic
representation, which doesn't seem right.
Would it work to say if line 1 and 2 are both checked,
then we want orthographic text also,
otherwise just normal text?
No, because then it wouldn't be possible to show only orthographic text.
Let's make line 2 be orthographic,
even though that won't be how it ends up being shown (unless a hidden option
is set?).

Change the grammar documentation to describe FieldWorks first.

[jkornelsen]

Finished in 4ddf01f.