Initial link box functionality

link.py contains the code for the link location selection box.
ExampleTwo has been added for testing link selection in future
Initial link window work

getNoteSummaries() returns the titles and subtitles of the notes in the
notes directory as a list

This will be used to display the notes so the correct one can be
selected for linking
Summaries of notes now obtained by link.py

This will allow a specific section of the notes to be linked to.
Also added exampleThree to make linking functionality easier to
demonstrate.
Further progress on link functionality

Linkbox now contains a list of the notes and rewrites in the notes
directory. Unfortunately the list is currently not scrollable despite a
scrollbar being there.
More added to link functionality

Equation button hidden, as it is not currently used
Added exampleFour.note to flesh out note list
Link window displaying improved
Moved link window to grid geometry manager

Link window now uses the grid geometry manager rather than the pack
manager.
Added frame style "HL.TFrame" for testing, which highlights the frame
red to ensure it is in the right place.
Modified link.py to use tkinter's askopenfilename

This avoids using a buggy custom list to display the files
A tkinter listbox will be used to display the selected file's titles and
subtitles
Made linkBox return a list with note name and line
Improved link.py error handling

Also completed link selecting functionality - actually linking to notes
still needs to be completed.
Added functions to textFrame to handle linking
Updated copyright notices
Fixed bug with highlighting text in either textbox

The different autoapplied tags were above the "sel" tag. Raising the
"sel" tag fixed the bug.
Further work on link insertion functionality

The link insertion functions will do different things depending on
whether there was a range of characters selected when starting the link.

If the characters were selected, it will apply the link tag to the
characters.
If there was nothing selected, it will simply insert the
name of the linked note, with the link tag applied, at the insert cursot
Initial linking functionality

Links can be created by pressing <Ctrl-l>
Currently links are forgotten upon changing tab, but the next few
commits will be working on keeping them saved upon tab change and saving
them with the file.

There are two options for saving them with the note:
    Separate file - causes cluttered notes directory
    Appended to bottom of note

Appended to the bottom of the note looks to be the better solution, as
it is cleaner, but if the user inspects the note with a text editor they
may change the links.
Updated openFile to scroll to the given line

If no line given, it will stay at the top

Rewrite box is now formatted when switched to to ensure it stays
formatted when switching between tabs or opening new notes
Further work on keeping links when switching tabs

Split insertLink function up so that it calls getLinkTag - this allows
me to call insertLink to insert a link without re-adding the link to the
hyperlink manager
Attempted to fix link storage on tab switch