Adding Autoinstall, JSX support, fixing a few minor things.

Thing we added

• Auto-install! You can now let the template install the dependencies for you right after the questionnaire:

This also runs npm run lint -- --fix, so all project files are automatically formatted according to the eslint config you chose (if any). That means we as the maintainers have a far easier time handling boilerplate files like HelloWorld.vue (since we don't have to accommodate the different eslint configs within those files), which means it will be easier and quicker to add new variations (e.g. typescript support, we'll see :) ).

• We now install babel-plugin-transform-vue-jsx and its peer dependencies by default, so JSX is not a first-class citizen for this template.

Things we improved

• the eslint config that is generated when choosing the Airbnb preset now comes with an adjusted rule that makes the preset play nice with Vuex state mutations. (#1003, @anubhav7495, adjusted by @LinusBorg with cc89353).

Things we fixed.

• Since babel-preset-env doesn't yet support browserslist in package.json until babel7 is released, we had to revert #1004, also added docs explaining this (1083, #144 thanks to @sudo-suhas)
• CSS from codesplit .vue files is now also extracted into the main .css file. Previously, it was contained in the codesplit chunk and inserted at runtime via vue-style-loader. That unfortunately has some (not vue-related) problems with sourcemaps. (See discussion here: #1110), (PR: #1149)