Upgrade to ember-cli@3.5

[ro0gr]

Updates internals to use ember/ember-cli of v3.5.

There is also some cleanup included, which is related to extending ignore files rules with assets produced by jekyll, etc..

The issue with upgrade is that with the new blueprint for some of ember-try scenarios we have jquery-integration feature set to off which makes old-style global testing helpers non-working.

Going to keep the following strategy:

• skip moduleFor tests if Ember.$ is not available
• re-write some of old tests from moduleForComponent to rendering tests
• re-enable jquery by default. This would allow to keep all the tests in the dev mode

[ro0gr]

Seems like some changes in the travis config re-enabled double CI build. travis-ci/push was disabled before this PR, will investiagate.

[coveralls]

Coverage increased (+0.1%) to 98.642% when pulling 738eae7 on ember-3.5 into 01bb5a5 on master.

[san650]

Good work @ro0gr 👏 ❤️