feat: RTL support

[kamaladenalhomsi]

Hi everyone!
in this PR, Vuesax is now supporting RTL completely!
I've checked every component, to make sure that the native LTR did not change,
and to make sure that each component supports RTL

How to use?

to activate RTL, you can pass the rtl option when calling function use()

import Vue from 'vue'
import Vuesax from 'vuesax'

Vue.use(Vuesax, {
  rtl: true
})

if you want to turn on or off RTL at any time, you can just write:

this.$vs.rtl = true // or false

this.$vs.rtl is also reactive, so you can use Vue watcher as below:

watch: {
  "$vs.rtl": {
     handler(val) {
      console.log(val)
    }
  }
}

Updates on Vuesax in this PR

RTL support feature based on two mixins, propWithDir & dirValue
I explained each one of them in the mixins.styl file, I hope you check it out
one of the major changes I did, that I used Vue.prototype._init function
to parse properties, and access the Vue instance, check override.js
I added a new file in

utils/rtl.js

this file contains the RTL logic,
the logic of the RTL is based on injecting vuesax-app-is-rtl class in the HTML element
in case of RTL, and it will Inject vuesax-app-is-ltr in ltr case,
the two mixins, propWithDir & dirValue, will create new two classes
one for the RTL, another one for the LTR directions
example:

.someClass
  propWithDir(padding, left, 10px)

[Compiled]

.vuesax-app-is-rtl
  .someClass
    padding-right: 10p

.vuesax-app-is-ltr
  .someClass
    padding-left: 10px

the full explanation of propWithDir & dirValue mixins in mixins.styl file

Resolve #93 #176 #581