Add plugin provider

[yann300]

This add the ability to reference new web3 provider.
Each "provider" plugin will be listed in the environment section of the run tab.

fix #30

Current state:

• with metamask, rejecting a transaction doesn't resolve the call in the client.

• sometimes gasEstimate returns a JSON RPC error (probably when the transaction fails), then force sending the transaction doesn't pop up anything in the mobile side.
  EDIT: https://github.com/ethereum/remix-project/pull/178/files#diff-b41d6048d9047202a90628384dd7d690R181

• can take more than 10 seconds for a call to resolve.
  we'll probably need if the problem persist to have our own bridge.

• call to a plugin can't be done asynchronously, so when a call doesn't resolve, all the other call to web3 are lined up (This probably can't be solved right now). this can't be solved. Plugin calls are synchronous (cc @GrandSchtroumpf fyi)

[iurimatias]

suggestion:

const provider = network.url === 'ipc' ? new Web3.providers.IpcProvider() : new Web3.providers.HttpProvider(network.url)
this.blockchain.addProvider({ name: network.name, provider })

[iurimatias]

is this really necessary (() => {})() it feels like it could be removed, and use this instead of app

[yann300]

this can be removed yes.
(() => {})() is to make sure the creation of the provider is encapsulated. (that the local var profile doesn't get overridden in case the event callback is triggered multiple time.
But there might be better way to handle that.

[yann300]

actually I had to keep this ...

[iurimatias]

suggestion: this.on('manager', 'pluginActivated', this.addProfileProvider.bind(this) and then move the code to that function

[iurimatias]

suggestion, something like:

async sendAsync (payload, callback) {
              console.log('wallet connect', payload)
              try {
                const result = await app.call(profile.name, 'sendAsync', payload)
                console.log('wallet connect', result)
                callback(null, result)
              } catch (e) {
                  console.log('wallet connect', e)
                  callback(e)
                })
}

[yann300]

@iurimatias just pushed some updates

[ryestew]

I like the update where you can have the walletconnect plugin as the active tab and the txn can still be run. The Clear Current Request button - is important - we'll see if users can find it - but if they find the button ( by realizing they should look at the walletconnect tab) then this will solve txns getting piled up. Also - I think the 2 min timeout works well - at least it worked for me.