minor #443 Validate user data before save (yceruto)
minor #443 Validate user data before save (yceruto)

This PR was squashed before being merged into the master branch (closes #443).

Discussion
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Validate user data before save

1. I've added a `validateUserData` method to check for existent user email (this improves a better messages exception) and validate plainPassword and email in non-interactive mode (i.e. `$ app:add-user username password email`).
2. Renamed the option `--is-admin` to just `--admin`, Imho `is-admin` feels more like a question rather than an instruction. (now `$ app:add-user username password email --admin`)

Any suggestion is welcome!

Commits
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7fc2fc1 Validate user data before save

symfony/symfony-demo,samitiana/symfony-demo,voronkovich/symfony-demo,bocharsky-bw/symfony-demo,Codeception/symfony-demo,maidmaid/symfony-demo,dzuelke/symfony-demo,dzuelke/symfony-demo,dzuelke/symfony-demo,samitiana/symfony-demo,javiereguiluz/symfony-demo,javiereguiluz/symfony-demo,maidmaid/symfony-demo,yodur2potassium/test-behat-selenium-symfo,voronkovich/symfony-demo,maidmaid/symfony-demo,bocharsky-bw/symfony-demo,samitiana/symfony-demo,yodur2potassium/test-behat-selenium-symfo,Codeception/symfony-demo,TomasVotruba/symfony-demo,Codeception/symfony-demo,voronkovich/symfony-demo,yodur2potassium/test-behat-selenium-symfo,yceruto/symfony-demo,yceruto/symfony-demo,yceruto/symfony-demo,javiereguiluz/symfony-demo,bocharsky-bw/symfony-demo,TomasVotruba/symfony-demo,TomasVotruba/symfony-demo,nilamkhedkar1/symfony_demo,nilamkhedkar1/symfony_demo,symfony/symfony-demo,symfony/symfony-demo,nilamkhedkar1/symfony_demo