Minimize shaded JARs

Configure 'maven-shade-plugin' to minimize shaded JARs. This reduces
the sizes of the applications as follows:

  - the terminal client: 10 MB to 5 MB (50% reduction)
  - the trading system: 17 MB to 1 MB (94% reduction)
  - the stock ticker: 17 MB to 1 MB (94% reduction)