docs(CONTRIBUTING): Update pull request guidelines
fix(tagsInput): Set element's validity when options change

Set element's validity when minTags, maxTags and allowLeftoverText
options change. Other validation options don't need to be monitored
because they are only used upon some user interaction with the directive.

Closes #154
refactor(tagsInput): Add default values to all options

Add default values to all options so some parts of the code become a
bit simpler by not having to check for 'undefined' before using an option.
Introduce a MAX_SAFE_INTEGER constant to be used as an upper bound for
maxTags and maxLength options.
chore(build): Update build files [skip ci]
fix(autocomplete): Fix suggestion selection on touch devices

Perform suggestion selection on mouse click instead of mouse enter so
it works correctly on touch devices.

Close #142
test(tagsInput): Add missing test

Add missing test to ensure the model is correctly initialized.
chore(build): Update build files [skip ci]
feat(tags Input): add support for pasting a collection of tags

This pullrequest adds functionality that allows a user to paste a
separated string instead of having to type all entries manually. the
pasted string will be parsed to tags and the invalid ones will be
discarded. The separators can be defined with the separatorList
attribute