login-page: Make the buttons and labels cleaner.
login-page: Make the buttons and labels cleaner.

Changes -
a) Updated the border-radius to 4px for all the buttons.
b) Increased the margins between the labels and inputs.

These changes affect the login and register page's styling.

shubhamdhama/zulip,rht/zulip,timabbott/zulip,timabbott/zulip,tommyip/zulip,punchagan/zulip,hackerkid/zulip,zulip/zulip,eeshangarg/zulip,showell/zulip,jackrzhang/zulip,zulip/zulip,hackerkid/zulip,synicalsyntax/zulip,hackerkid/zulip,kou/zulip,hackerkid/zulip,tommyip/zulip,jackrzhang/zulip,kou/zulip,punchagan/zulip,jackrzhang/zulip,tommyip/zulip,andersk/zulip,hackerkid/zulip,zulip/zulip,andersk/zulip,andersk/zulip,zulip/zulip,shubhamdhama/zulip,zulip/zulip,punchagan/zulip,zulip/zulip,dhcrzf/zulip,timabbott/zulip,shubhamdhama/zulip,eeshangarg/zulip,dhcrzf/zulip,showell/zulip,rishig/zulip,brainwane/zulip,rht/zulip,hackerkid/zulip,eeshangarg/zulip,andersk/zulip,rht/zulip,brainwane/zulip,rishig/zulip,brainwane/zulip,showell/zulip,rht/zulip,eeshangarg/zulip,eeshangarg/zulip,kou/zulip,tommyip/zulip,synicalsyntax/zulip,rht/zulip,brainwane/zulip,dhcrzf/zulip,shubhamdhama/zulip,punchagan/zulip,dhcrzf/zulip,tommyip/zulip,jackrzhang/zulip,kou/zulip,timabbott/zulip,jackrzhang/zulip,punchagan/zulip,shubhamdhama/zulip,tommyip/zulip,jackrzhang/zulip,brainwane/zulip,dhcrzf/zulip,kou/zulip,rishig/zulip,eeshangarg/zulip,synicalsyntax/zulip,kou/zulip,timabbott/zulip,showell/zulip,andersk/zulip,hackerkid/zulip,synicalsyntax/zulip,rht/zulip,timabbott/zulip,punchagan/zulip,dhcrzf/zulip,showell/zulip,tommyip/zulip,andersk/zulip,showell/zulip,rishig/zulip,eeshangarg/zulip,synicalsyntax/zulip,zulip/zulip,showell/zulip,kou/zulip,brainwane/zulip,andersk/zulip,dhcrzf/zulip,punchagan/zulip,jackrzhang/zulip,timabbott/zulip,synicalsyntax/zulip,rishig/zulip,rht/zulip,rishig/zulip,brainwane/zulip,shubhamdhama/zulip,synicalsyntax/zulip,shubhamdhama/zulip,rishig/zulip