Add option to display line numbers

[Justaphf]

Adds a user option to display simple line number prefixes in the tails display window.

Features:

• Ability to turn on/off display of line numbers per-file config.
• Ability to apply line number display setting to all open logs (apply all).
• Ability to set line number display option as a global default preference for newly opened configs.
• When turned on, line numbers draw as a right-aligned prefix to each line with ": " between the line number and line content.
  • NOTE: Right alignment is 10 character width, which supports 2^32 (~2 billion) line numbers supported by 32-bit signed integer, without thousands separators.
• Truncation for lines has been updated such that truncation now takes into account inclusion of the line number & separator to ensure whole line width stays within the pre-existing 1000 character limit.
• Line numbers are 1 indexed based on the index in the list item virtual cache (index + 1).
  • NOTE: This assumes that this absolute index is correct in terms of position in source file and display in the tails window.

Testing:

• Tested with a continuous append log file up to ~3 million lines.
• Tested scrolling to begin/end of tails with
• Tested scrolling to random sampling of positions within log file
• Tested deleting a set of middle lines from log
  • NOTE: Update seemed to work correctly, however the update was slower than simple append updates and fast navigation to distant locations in the log as the entire file was reloaded & lines recalculated (existing functionality).

[Justaphf]

Partial fix of request #26 for line numbers. Does not fix word wrap.