Improve example scripts

[bwohlberg]

The example scripts could do with improvement on a number of fronts

• Where isotropic TV is used, change regularization term notation from ||Cx||_1 to ||Cx||_{2,1}.
• Script (and corresponding notebook) names could be simplified (e.g. does the iso in some TV examples really play a useful role?).
• Script titles could be more consistent (e.g. most include details such as optimizer used in parentheses, but some do not).
• Some of the scripts have excessively brief initial descriptions of the purpose of the example.
• Greater consistency in the initial descriptions would be desirable (e.g. always provide both the functional being minimized and link(s) to relevant scico classes).
• More detail could be provided in setting up the functionals to be solved, and it would also be helpful to explain the choice of optimization algorithm.
• Some script names and titles could be improved (e.g. "Isotropic Total Variation" actually compares isotropic and anisotropic forms).