jetson_config, new environment variables, improved jtop

This new release improve the performance of jtop

New script jetson_config available on your shell:

• manage the health of this package
• enable/disable desktop
• improve wifi
• control jetson_clocks (like jtop)

Fix some bugs:

• jtop not working #49
• Check status jetson_clocks #36
• jtop should not print Total value as sum of POM_5V_IN, POM_5V_GPU and POM_5V_CPU #51