Implement find / replace feature

[njourdane]

A common feature in IDEs and text editors in general: ability to find a pattern, and to replace a pattern by an other.

Good IDEs allow to find/replace a pattern by regex, including back-reference groups (Intellij's behavior can be a good inspiration source for this).

[njourdane]

Also, here are good keyboard shortcut candidates, used in many text editors:

• ctrl + F: find
• ctrl + R: replace
• F3: find next
• ctrl + F3: find previous