Allow tweets to exceed 280 character limit

[jdubpark]

Currently, the Twitter connection enforces the text length to be less than 280 (_validate_tweet_text). More complex tweets exceeding that limit can use Tweet threads. For instance, post a tweet of 280 characters and then a sub-tweet with another 280 characters.

[ayoubed]

Agreed, the feature should be either:

• post over 280 chars if the account is pro
• post a thread if not.