Option for current tab number to secondary section

[macownersclub]

option:

The number of the current tab is displayed to the right (secondary section) in the form of -1-. This will happen only if:

• tab-bar-mode is enabled
• the custom variable nano-modeline-display-tab-number is set to t and
• there are more than 1 tab open

changes to files:

• nano-modeline.el:
  • Add custom variable nano-modeline-display-tab-number
  • Add function nano-modeline-tab-number
  • Modify function nano-modeline-render

[macownersclub]

Note that this PR is limited to 7d9430f641933b7e01a44cf6449874999045a924. The other commits are just some stuff I am trying.

[macownersclub]

Closing and doing it right with: #44