Fix duplicate child routes with PREFIX_AND_DEFAULT strategy (fixes #292)

[rchl]

Fixes two problems when using PREFIX_AND_DEFAULT strategy:

• parent route with child routes had strange name like
  'undefined__default'. Fixed by not appending default suffix if route
  has children. Such routes don't need name as navigating to them
  wouldn't really work properly anyway (need to navigate to child
  route).

• Extra child routes were added with 'default' suffix. Fixed by not
  adding extra routes in children arrays. Those don't make sense as
  only parent routes should have extra route with no locale prefix.

[codecov]

Codecov Report

Merging #294 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master   #294   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           2      2           
  Lines           4      4           
=====================================
  Hits            4      4

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[aldarund]

What router.js will be generated for childrens after that pr?

[rchl]

With #292 testcase, routes will look like this:

    routes: [{
      path: "/about",
      component: _b6e37380,
      name: "about___en-us___default"
    }, {
      path: "/en-us/about",
      component: _b6e37380,
      name: "about___en-us"
    }, {
      path: "/fr/about",
      component: _b6e37380,
      name: "about___fr"
    }, {
      path: "/account",
      component: _2479bbc0,
      children: [{
        path: "child",
        component: _8329b026,
        name: "account-child___en-us___default"
      }]
    }, {
      path: "/en-us/account",
      component: _2479bbc0,
      children: [{
        path: "child",
        component: _8329b026,
        name: "account-child___en-us"
      }]
    }, {
      path: "/fr/account",
      component: _2479bbc0,
      children: [{
        path: "child",
        component: _8329b026,
        name: "account-child___fr"
      }]
    }, {
      path: "/",
      component: _7773bdf6,
      name: "index___en-us___default"
    }, {
      path: "/en-us/",
      component: _7773bdf6,
      name: "index___en-us"
    }, {
      path: "/fr/",
      component: _7773bdf6,
      name: "index___fr"
    }],

[aldarund]

lgtm

[paulgv]

Thank you @rchl!