Bug 916100 - [Contacts] Taapping on the disabled merge button when there are not contacts selected to be merged make it to change its colour.
Bug 910170 - [CONTACTS] The export button isn't disabled when no contact is selected.
Merge pull request #12295 from gtorodelvalle/contacts-bug-916100-footer-button-not-disabled

Bug 916100 - [Contacts] Taapping on the disabled merge button when there are not contacts selected to be merged make it to change its colour (r=jmcanterafonseca)
Merge pull request #12296 from gtorodelvalle/contacts-bug-910170-export-button-not-disabled

Bug 910170 - [CONTACTS] The export button isn't disabled when no contact is selected (r=jmcanterafonseca).
Bug 885713 - propose a "make hint" that would use jshint instead of gjslint

This adds
* a default .jshintrc configuration file
* a `make hint` launcher
* a way to launch the linters (including the old lint linter) for a specific app
  only.
* you can also use another jshint configuration file
use jshintignore
use one .jshintignore instead of external files
use npm to install jshint
remove b2g and tools directories that did not match anything before anyway