Improve input field in discussion

[dbrugne]

• [x] Try multiline, when message is on multiple line TextInput should be heigher (with max-height), read carefully doc to identify caveats with multiline
• [x] Increase font size in TextInput
• [x] When submit message with empty line(s) at end remove all empty lines spaces at end of message
• [x] When submitting message, until request response, grey input and block submit button to avoid multi submitting