Chats: Implemented autosizing textarea using react-textarea-autosize component

Fixes #380 (closed) and #426 (closed)

Added react-textarea-autosize component to implement the solution. Removed resize control from bottom rt of textarea. Tested vertical scrollbar, but got momentary blink of scrollbar on each textarea height adjustment.

Added hover tooltip on chats list to display content of last chat message. Solved issue of some chat posts not allowing SCSS to render one-line clamping on last message display in chats list.