recent_topics: Fix % of space taken by columns.
recent_topics: Fix % of space taken by columns.

This stops recent topics from adjusting column widths as new
messages are fetched, resulting in a better user experience.

andersk/zulip,zulip/zulip,punchagan/zulip,zulip/zulip,zulip/zulip,zulip/zulip,andersk/zulip,hackerkid/zulip,punchagan/zulip,andersk/zulip,kou/zulip,andersk/zulip,zulip/zulip,kou/zulip,rht/zulip,zulip/zulip,rht/zulip,zulip/zulip,eeshangarg/zulip,kou/zulip,eeshangarg/zulip,punchagan/zulip,hackerkid/zulip,rht/zulip,kou/zulip,eeshangarg/zulip,punchagan/zulip,andersk/zulip,eeshangarg/zulip,kou/zulip,hackerkid/zulip,hackerkid/zulip,punchagan/zulip,punchagan/zulip,rht/zulip,hackerkid/zulip,kou/zulip,rht/zulip,kou/zulip,andersk/zulip,andersk/zulip,punchagan/zulip,rht/zulip,rht/zulip,hackerkid/zulip,hackerkid/zulip,eeshangarg/zulip,eeshangarg/zulip,eeshangarg/zulip